arm_core_mpu.h and arm_core_mpu.c defined and implement kernel
APIs for memory protection, respectively. Therefore, they do not
need to directly include ARM CMSIS headers, or arm_mpu.h (or
nxp_mpu.h) which are supposed to define MPU-related kernel types
and convenience macros for the specific MPU architecture. These
headers are indirectly included by including kernel.h.
Similarly, arm_mpu.h shall not need to include internal/external
headers of memory protection APIs.
Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>