teensy: Add own uart.h to not rely on stm32's version of the file.
teensy: Add own uart.h to not rely on stm32's version of the file.

pozetroninc/micropython,henriknelson/micropython,tobbad/micropython,henriknelson/micropython,trezor/micropython,pfalcon/micropython,selste/micropython,kerneltask/micropython,pramasoul/micropython,adafruit/circuitpython,MrSurly/micropython,bvernoux/micropython,bvernoux/micropython,adafruit/circuitpython,pozetroninc/micropython,MrSurly/micropython,henriknelson/micropython,bvernoux/micropython,bvernoux/micropython,pozetroninc/micropython,kerneltask/micropython,pfalcon/micropython,MrSurly/micropython,pramasoul/micropython,selste/micropython,pramasoul/micropython,trezor/micropython,pozetroninc/micropython,pramasoul/micropython,selste/micropython,tobbad/micropython,kerneltask/micropython,adafruit/circuitpython,MrSurly/micropython,kerneltask/micropython,bvernoux/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,MrSurly/micropython,selste/micropython,tobbad/micropython,selste/micropython,henriknelson/micropython,adafruit/circuitpython,trezor/micropython,adafruit/circuitpython,henriknelson/micropython,tobbad/micropython,tobbad/micropython,trezor/micropython,adafruit/circuitpython,pramasoul/micropython,kerneltask/micropython,pozetroninc/micropython,trezor/micropython