make access to CP register volatile so it doesn't get optimised out
make access to CP register volatile so it doesn't get optimised out

ARM-software/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,ARM-software/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5