Vector table must be 256 aligned
Vector table must be 256 aligned

The vector table must be 256 aligned to work reliably, it must have been working by accident up to now.  This modification tested on a u-blox c027 board.  Without the change the value of `SCB->VTOR` and int_table are as follows:

`SCB->VTOR 0x10000280, int_table 0x100002a0`

...with the change they are as follows:

`SCB->VTOR 0x10000400, int_table 0x10000400`

...and the test passes.

See issue:

https://github.com/mbedmicro/mbed/issues/992
pedromes/mbed,logost/mbed,mmorenobarm/mbed-os,naves-thiago/mbed-midi,ryankurte/mbed-os,nvlsianpu/mbed,adustm/mbed,wodji/mbed,K4zuki/mbed,radhika-raghavendran/mbed-os5.1-onsemi,catiedev/mbed-os,EmuxEvans/mbed,fvincenzo/mbed-os,ryankurte/mbed-os,jrjang/mbed,nabilbendafi/mbed,ryankurte/mbed-os,mbedmicro/mbed,NXPmicro/mbed,fpiot/mbed-ats,CalSol/mbed,hwfwgrp/mbed,devanlai/mbed,svastm/mbed,autopulated/mbed,JasonHow44/mbed,pbrook/mbed,HeadsUpDisplayInc/mbed,theotherjimmy/mbed,bikeNomad/mbed,Shengliang/mbed,j-greffe/mbed-os,rosterloh/mbed,nRFMesh/mbed-os,jamesadevine/mbed,pradeep-gr/mbed-os5-onsemi,ARM-software/mbed-beetle,HeadsUpDisplayInc/mbed,wodji/mbed,hwfwgrp/mbed,naves-thiago/mbed-midi,devanlai/mbed,geky/mbed,mazimkhan/mbed-os,NXPmicro/mbed,fahhem/mbed-os,monkiineko/mbed-os,mnlipp/mbed,getopenmono/mbed,kpurusho/mbed,al177/mbed,pbrook/mbed,fanghuaqi/mbed,mnlipp/mbed,devanlai/mbed,ARM-software/mbed-beetle,Sweet-Peas/mbed,Shengliang/mbed,struempelix/mbed,larks/mbed,jrjang/mbed,CalSol/mbed,screamerbg/mbed,wodji/mbed,al177/mbed,xcrespo/mbed,theotherjimmy/mbed,kjbracey-arm/mbed,tung7970/mbed-os-1,logost/mbed,struempelix/mbed,larks/mbed,maximmbed/mbed,K4zuki/mbed,Marcomissyou/mbed,infinnovation/mbed-os,pbrook/mbed,mbedmicro/mbed,al177/mbed,infinnovation/mbed-os,hwfwgrp/mbed,masaohamanaka/mbed,jamesadevine/mbed,NitinBhaskar/mbed,geky/mbed,netzimme/mbed-os,fpiot/mbed-ats,karsev/mbed-os,brstew/MBED-BUILD,tung7970/mbed-os-1,betzw/mbed-os,NitinBhaskar/mbed,getopenmono/mbed,Sweet-Peas/mbed,andcor02/mbed-os,svogl/mbed-os,kjbracey-arm/mbed,kl-cruz/mbed-os,mmorenobarm/mbed-os,andreaslarssonublox/mbed,fvincenzo/mbed-os,pradeep-gr/mbed-os5-onsemi,jferreir/mbed,rgrover/mbed,xcrespo/mbed,maximmbed/mbed,RonEld/mbed,YarivCol/mbed-os,autopulated/mbed,Archcady/mbed-os,nabilbendafi/mbed,JasonHow44/mbed,nRFMesh/mbed-os,jeremybrodt/mbed,logost/mbed,theotherjimmy/mbed,adamgreen/mbed,larks/mbed,jferreir/mbed,CalSol/mbed,alertby/mbed,getopenmono/mbed,j-greffe/mbed-os,Marcomissyou/mbed,jferreir/mbed,NitinBhaskar/mbed,andcor02/mbed-os,monkiineko/mbed-os,catiedev/mbed-os,wodji/mbed,hwfwgrp/mbed,pi19404/mbed,ban4jp/mbed,mbedmicro/mbed,jpbrucker/mbed,karsev/mbed-os,betzw/mbed-os,EmuxEvans/mbed,adustm/mbed,wodji/mbed,nRFMesh/mbed-os,mmorenobarm/mbed-os,nvlsianpu/mbed,pi19404/mbed,al177/mbed,jrjang/mbed,masaohamanaka/mbed,arostm/mbed-os,jrjang/mbed,netzimme/mbed-os,brstew/MBED-BUILD,CalSol/mbed,Archcady/mbed-os,ryankurte/mbed-os,xcrespo/mbed,alertby/mbed,Marcomissyou/mbed,Shengliang/mbed,nabilbendafi/mbed,radhika-raghavendran/mbed-os5.1-onsemi,andreaslarssonublox/mbed,DanKupiniak/mbed,masaohamanaka/mbed,NXPmicro/mbed,nRFMesh/mbed-os,RonEld/mbed,catiedev/mbed-os,K4zuki/mbed,mikaleppanen/mbed-os,geky/mbed,Marcomissyou/mbed,jeremybrodt/mbed,logost/mbed,kjbracey-arm/mbed,cvtsi2sd/mbed-os,masaohamanaka/mbed,bcostm/mbed-os,Tiryoh/mbed,mazimkhan/mbed-os,dbestm/mbed,jamesadevine/mbed,struempelix/mbed,Tiryoh/mbed,jamesadevine/mbed,geky/mbed,autopulated/mbed,rosterloh/mbed,betzw/mbed-os,cvtsi2sd/mbed-os,cvtsi2sd/mbed-os,tung7970/mbed-os,bikeNomad/mbed,jrjang/mbed,YarivCol/mbed-os,xcrespo/mbed,Tiryoh/mbed,pradeep-gr/mbed-os5-onsemi,NXPmicro/mbed,netzimme/mbed-os,bcostm/mbed-os,svogl/mbed-os,YarivCol/mbed-os,Archcady/mbed-os,mazimkhan/mbed-os,betzw/mbed-os,kl-cruz/mbed-os,mikaleppanen/mbed-os,HeadsUpDisplayInc/mbed,maximmbed/mbed,bikeNomad/mbed,geky/mbed,nRFMesh/mbed-os,andcor02/mbed-os,radhika-raghavendran/mbed-os5.1-onsemi,ryankurte/mbed-os,ARM-software/mbed-beetle,Sweet-Peas/mbed,svogl/mbed-os,bulislaw/mbed-os,bcostm/mbed-os,mikaleppanen/mbed-os,getopenmono/mbed,fvincenzo/mbed-os,karsev/mbed-os,bulislaw/mbed-os,kpurusho/mbed,EmuxEvans/mbed,fvincenzo/mbed-os,fanghuaqi/mbed,andcor02/mbed-os,arostm/mbed-os,nvlsianpu/mbed,bikeNomad/mbed,Sweet-Peas/mbed,pbrook/mbed,kpurusho/mbed,c1728p9/mbed-os,wodji/mbed,alertby/mbed,Archcady/mbed-os,bcostm/mbed-os,kpurusho/mbed,radhika-raghavendran/mbed-os5.1-onsemi,theotherjimmy/mbed,fpiot/mbed-ats,Shengliang/mbed,adustm/mbed,pedromes/mbed,mnlipp/mbed,logost/mbed,theotherjimmy/mbed,YarivCol/mbed-os,catiedev/mbed-os,Timmmm/mbed,jeremybrodt/mbed,JasonHow44/mbed,kl-cruz/mbed-os,nvlsianpu/mbed,mnlipp/mbed,HeadsUpDisplayInc/mbed,pi19404/mbed,pradeep-gr/mbed-os5-onsemi,DanKupiniak/mbed,monkiineko/mbed-os,ban4jp/mbed,jpbrucker/mbed,Archcady/mbed-os,jpbrucker/mbed,adamgreen/mbed,andreaslarssonublox/mbed,screamerbg/mbed,netzimme/mbed-os,andreaslarssonublox/mbed,theotherjimmy/mbed,alertby/mbed,autopulated/mbed,screamerbg/mbed,tung7970/mbed-os-1,autopulated/mbed,YarivCol/mbed-os,j-greffe/mbed-os,EmuxEvans/mbed,svastm/mbed,fanghuaqi/mbed,mazimkhan/mbed-os,hwfwgrp/mbed,tung7970/mbed-os-1,nabilbendafi/mbed,naves-thiago/mbed-midi,Timmmm/mbed,K4zuki/mbed,JasonHow44/mbed,jpbrucker/mbed,j-greffe/mbed-os,jeremybrodt/mbed,alertby/mbed,cvtsi2sd/mbed-os,devanlai/mbed,bulislaw/mbed-os,fpiot/mbed-ats,rosterloh/mbed,pradeep-gr/mbed-os5-onsemi,ryankurte/mbed-os,rgrover/mbed,nvlsianpu/mbed,mikaleppanen/mbed-os,andcor02/mbed-os,bentwire/mbed,mikalepp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