stm: Disable usart calls from C.
stm: Disable usart calls from C.

Fixes Issue #132.

SungEun-Steve-Kim/test-mp,dinau/micropython,utopiaprince/micropython,oopy/micropython,aethaniel/micropython,alex-march/micropython,xhat/micropython,vriera/micropython,alex-march/micropython,cloudformdesign/micropython,alex-robbins/micropython,EcmaXp/micropython,chrisdearman/micropython,ryannathans/micropython,chrisdearman/micropython,deshipu/micropython,vitiral/micropython,noahwilliamsson/micropython,neilh10/micropython,SungEun-Steve-Kim/test-mp,turbinenreiter/micropython,rubencabrera/micropython,xyb/micropython,xuxiaoxin/micropython,trezor/micropython,dhylands/micropython,orionrobots/micropython,matthewelse/micropython,infinnovation/micropython,xyb/micropython,suda/micropython,drrk/micropython,PappaPeppar/micropython,torwag/micropython,aethaniel/micropython,tuc-osg/micropython,mpalomer/micropython,mhoffma/micropython,lowRISC/micropython,adafruit/circuitpython,misterdanb/micropython,ernesto-g/micropython,cwyark/micropython,jlillest/micropython,noahwilliamsson/micropython,SungEun-Steve-Kim/test-mp,Timmenem/micropython,matthewelse/micropython,ruffy91/micropython,ahotam/micropython,tralamazza/micropython,mgyenik/micropython,torwag/micropython,cwyark/micropython,tobbad/micropython,galenhz/micropython,xhat/micropython,jmarcelino/pycom-micropython,emfcamp/micropython,PappaPeppar/micropython,neilh10/micropython,Peetz0r/micropython-esp32,dinau/micropython,blmorris/micropython,rubencabrera/micropython,praemdonck/micropython,cnoviello/micropython,hosaka/micropython,dxxb/micropython,torwag/micropython,utopiaprince/micropython,dhylands/micropython,dxxb/micropython,HenrikSolver/micropython,skybird6672/micropython,martinribelotta/micropython,kerneltask/micropython,noahwilliamsson/micropython,AriZuu/micropython,chrisdearman/micropython,heisewangluo/micropython,jlillest/micropython,bvernoux/micropython,oopy/micropython,henriknelson/micropython,feilongfl/micropython,hiway/micropython,Vogtinator/micropython,supergis/micropython,pfalcon/micropython,matthewelse/micropython,oopy/micropython,paul-xxx/micropython,blmorris/micropython,redbear/micropython,pramasoul/micropython,puuu/micropython,heisewangluo/micropython,ericsnowcurrently/micropython,aethaniel/micropython,utopiaprince/micropython,mianos/micropython,jlillest/micropython,tdautc19841202/micropython,henriknelson/micropython,adamkh/micropython,cloudformdesign/micropython,vitiral/micropython,redbear/micropython,warner83/micropython,dhylands/micropython,warner83/micropython,noahwilliamsson/micropython,ericsnowcurrently/micropython,toolmacher/micropython,skybird6672/micropython,pozetroninc/micropython,danicampora/micropython,skybird6672/micropython,praemdonck/micropython,Vogtinator/micropython,chrisdearman/micropython,puuu/micropython,redbear/micropython,danicampora/micropython,adafruit/circuitpython,AriZuu/micropython,puuu/micropython,kostyll/micropython,lowRISC/micropython,Timmenem/micropython,ganshun666/micropython,feilongfl/micropython,cwyark/micropython,adafruit/micropython,methoxid/micropystat,orionrobots/micropython,tralamazza/micropython,jlillest/micropython,feilongfl/micropython,dinau/micropython,jimkmc/micropython,mgyenik/micropython,SHA2017-badge/micropython-esp32,infinnovation/micropython,suda/micropython,PappaPeppar/micropython,MrSurly/micropython-esp32,dxxb/micropython,kerneltask/micropython,deshipu/micropython,Timmenem/micropython,turbinenreiter/micropython,firstval/micropython,Vogtinator/micropython,praemdonck/micropython,micropython/micropython-esp32,noahchense/micropython,martinribelotta/micropython,omtinez/micropython,martinribelotta/micropython,MrSurly/micropython,MrSurly/micropython,adamkh/micropython,vitiral/micropython,misterdanb/micropython,xhat/micropython,swegener/micropython,jimkmc/micropython,cnoviello/micropython,adafruit/micropython,adamkh/micropython,jimkmc/micropython,jmarcelino/pycom-micropython,mianos/micropython,ryannathans/micropython,ganshun666/micropython,EcmaXp/micropython,TDAbboud/micropython,ryannathans/micropython,rubencabrera/micropython,pfalcon/micropython,ChuckM/micropython,SungEun-Steve-Kim/test-mp,EcmaXp/micropython,mhoffma/micropython,cloudformdesign/micropython,aethaniel/micropython,utopiaprince/micropython,vriera/micropython,slzatz/micropython,stonegithubs/micropython,redbear/micropython,emfcamp/micropython,jmarcelino/pycom-micropython,dmazzella/micropython,SungEun-Steve-Kim/test-mp,pramasoul/micropython,ernesto-g/micropython,deshipu/micropython,stonegithubs/micropython,ryannathans/micropython,alex-march/micropython,vitiral/micropython,ruffy91/micropython,tuc-osg/micropython,orionrobots/micropython,mianos/micropython,tobbad/micropython,cloudformdesign/micropython,tdautc19841202/micropython,micropython/micropython-esp32,SHA2017-badge/micropython-esp32,pramasoul/micropython,ceramos/micropython,Peetz0r/micropython-esp32,warner83/micropython,mgyenik/micropython,ryannathans/micropython,tdautc19841202/micropython,emfcamp/micropython,Timmenem/micropython,TDAbboud/micropython,mpalomer/micropython,dmazzella/micropython,ceramos/micropython,KISSMonX/micropython,ericsnowcurrently/micropython,pozetroninc/micropython,bvernoux/micropython,hiway/micropython,blmorris/micropython,misterdanb/micropython,pozetroninc/micropython,MrSurly/micropython-esp32,henriknelson/micropython,kostyll/micropython,toolmacher/micropython,bvernoux/micropython,neilh10/micropython,mpalomer/micropython,ganshun666/micropython,ganshun666/micropython,MrSurly/micropython,alex-march/micropython,redbear/micropython,tralamazza/micropython,xyb/micropython,micropython/micropython-esp32,omtinez/micropython,infinnovation/micropython,emfcamp/micropython,trezor/micropython,EcmaXp/micropython,supergis/micropython,kerneltask/micropython,HenrikSolver/micropython,TDAbboud/micropython,swegener/micropython,drrk/micropython,galenhz/micropython,matthewelse/micropython,orionrobots/micropython,hosaka/micropython,praemdonck/micropython,paul-xxx/micropython,selste/micropython,hiway/micropython,PappaPeppar/micropython,xyb/micropython,jlillest/micropython,blmorris/micropython,aitjcize/micropython,xhat/micropython,lbattraw/micropython,adafruit/circuitpython,supergis/micropython,puuu/micropython,ernesto-g/micropython,jimkmc/micropython,kerneltask/micropython,tuc-osg/micropython,skybird6672/micropython,heisewangluo/micropython,kerneltask/micropython,mianos/micropython,ceramos/micropython,lowRISC/micropython,henriknelson/micropython,xyb/micropython,noahchense/micropython,xuxiaoxin/micropython,KISSMonX/micropython,tralamazza/micropython,MrSurly/micropython-esp32,adamkh/micropython,mianos/micropython,ernesto-g/micropython,suda/micropython,vriera/micropython,pramasoul/micropython,slzatz/micropython,dxxb/micropython,henriknelson/micropython,ahotam/micropython,cnoviello/micropython,TDAbboud/micropython,pramasoul/micropython,AriZuu/micropython,omtinez/micropython,toolmacher/micropython,cwyark/micropython,drrk/micropython,blazewicz/micropython,drrk/micropython,HenrikSolver/micropython,MrSurly/micropython,infinnovation/micropython,dinau/micropython,neilh10/micropython,swegener/micropython,MrSurly/micropython,galenhz/micropython,danicampora/micropython,omtinez/micropython,methoxid/micropystat,ahotam/micropython,hosaka/micropython,pfalcon/micropython,HenrikSolver/micropython,jmarcelino/pycom-micropython,selste/micropython,alex-robbins/micropython,adafruit/circuitpython,ruffy91/micropython,AriZuu/micropython,dxxb/micropython,xuxiaoxin/micropython,ganshun666/micropython,ruffy91/micropython,blazewicz/micropython,cnoviello/micropython,aitjcize/micropython,feilongfl/micropython,dhylands/micropython,blazewicz/micropython,methoxid/micropystat,bvernoux/micropython,warner83/micropython,dmazzella/micropython,MrSurly/micropython-esp32,suda/micropython,dhylands/micropython,ahotam/micropython,HenrikSolver/micropython,martinribelotta/micropython,cnoviello/micropython,selste/micropython,pozetroninc/micropython,chrisdearman/micropython,mhoffma/micropython,kostyll/micropython,paul-xxx/micropython,mpalomer/micropython,noahwilliamsson/micropython,TDAbboud/micropython,torwag/micropython,mhoffma/micropython,torwag/micropython,feilongfl/micropython,ChuckM/micropython,oopy/micropython,skybird6672/micropython,adafruit/circuitpython,firstval/micropython,warner83/micropython,praemdonck/micropython,swegener/micropython,tdautc19841202/micropython,alex-march/micropython,ChuckM/micropython,suda/micropython,martinribelotta/micropython,SHA2017-badge/micropython-esp32,Peetz0r/micropython-esp32,jmarcelino/pycom-micropython,puuu/micropython,cwyark/micropython,Peetz0r/micropython-esp32,pozetroninc/micropython,adamkh/micropython,lowRISC/micropython,orionrobots/micropython,lbattraw/micropython,aethaniel/micropython,tdautc19841202/micropython,tobbad/micropython,drrk/micropython,omtinez/micropython,infinnovation/micropython,oopy/micropython,KISSMonX/micropython,vitiral/micropython,toolmacher/micropython,matthewelse/micropython,rubencabrera/micropython,adafruit/circuitpython,tobbad/micropython,toolmacher/micropython,aitjcize/micropython,Peetz0r/micropython-esp32,tuc-osg/micropython,mgyenik/micropython,selste/micropython,cloudformdesign/micropython,mpalomer/micropython,galenhz/micropython,Timmenem/micropython,Vogtinator/micropython,slzatz/micropython,rubencabrera/micropython,jimkmc/micropython,ernesto-g/micropython,KISSMonX/micropython,ceramos/micropython,blmorris/micropython,dmazzella/micropython,hosaka/micropython,dinau/micropython,AriZuu/micropython,emfcamp/micropython,vriera/micropython,deshipu/micropython,ceramos/micropython,turbinenreiter/micropython,matthewelse/micropython,deshipu/micropython,PappaPeppar/micropython,mhoffma/micropython,hiway/micropython,danicampora/micropython,adafruit/micropython,trezor/micropython,noahchense/micropython,methoxid/micropystat,firstval/micropython,ruffy91/micropython,xhat/micropython,SHA2017-badge/micropython-esp32,aitjcize/micropython,lbattraw/micropython,noahchense/micropython,trezor/micropython,EcmaXp/micropython,firstval/micropython,adafruit/micropython,trezor/micropython,hosaka/micropython,slzatz/micropython,ChuckM/micropython,mgyenik/micropython,misterdanb/micropython,stonegithubs/micropython,ericsnowcurrently/micropython,danicampora/micropython,heisewangluo/micropython,kostyll/micropython,tobbad/micropython,lbattraw/micropython,pfalcon/micropython,pfalcon/micropython,misterdanb/micropython,xuxiaoxin/micropython,MrSurly/micropython-esp32,swegener/micropython,turbinenreiter/micropython,selste/micropython,heisewangluo/micropython,blazewicz/micropython,alex-robbins/micropython,paul-xxx/micropython,ahotam/micropython,Vogtinator/micropython,supergis/micropython,methoxid/micropystat,alex-robbins/micropython,alex-robbins/micropython,KISSMonX/micropython,blazewicz/micropython,neilh10/micropython,noahchense/micropython,lbattraw/micropython,SHA2017-badge/micropython-esp32,micropython/micropython-esp32,tuc-osg/micropython,supergis/micropython,hiway/micropython,utopiaprince/micropython,slzatz/micropython,ericsnowcurrently/micropython,lowRISC/micropython,stonegithubs/micropython,vriera/micropython,galenhz/micropython,bvernoux/micropython,paul-xxx/micropython,turbinenreiter/micropython,kostyll/micropython,firstval/micropython,ChuckM/micropython,xuxiaoxin/micropython,adafruit/micropython,stonegithubs/micropython,micropython/micropython-esp32