Unlike Cortex-M3 and Cortex-M4, in Cortex-M7 the number of
MPU regions may vary based on the implementation. This commit
adds a DTS node for the ARM MPU peripheral in the device tree
of Cortex-M7 SoCs and updates the fixup files, so we may extract
the number of MPU regions at build time. SoCs:
- nxp_rt
- same70
- stm32f7
Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>