CMSIS/RTX: Reintroduce arm_math.h
CMSIS/RTX: Reintroduce arm_math.h

(cherry picked from commit 6a6e3ac0ebab1a6b6aa08d0928702c79562acee9)

mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,mbedmicro/mbed,andcor02/mbed-os,kjbracey-arm/mbed,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,mbedmicro/mbed,kjbracey-arm/mbed