arch: mem protect Kconfig cleanups

Adds a new CONFIG_MPU which is set if an MPU is enabled. This
is a menuconfig will some MPU-specific options moved
under it.

MEMORY_PROTECTION and SRAM_REGION_PERMISSIONS have been merged.
This configuration depends on an MMU or MPU. The protection
test is updated accordingly.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
6 files changed