FreeRTOS MPU: Remove MPU region number check (#1261)

FreeRTOS MPU: Remove MPU region number check

This change removes the assertion and runtime check that enforces
matching between configTOTAL_MPU_REGIONS and physical MPU
regions,. This allows applications running on devices with 16 MPU
regions to manage 8 MPU regions while leaving the remaining 8
for the kernel.

Signed-off-by: Erick Reyes <erickreyes@google.com>

Author: ErickReyesR