* add arc mpu driver
* modify the corresponding kconfig and kbuild
* currently only em_starterkit 2.2's em7d configuration
has mpu feature (mpu version 2)
* as the minimum region size of arc mpu version 2 is 2048 bytes and
region size should be power of 2, the stack size of threads
(including main thread and idle thread) should be at least
2048 bytes and power of 2
* for mpu stack guard feature, a stack guard region of 2048 bytes
is generated. This brings more memory footprint
* For arc mpu version 3, the minimum region size is 32 bytes.
* the codes are tested by the mpu_stack_guard_test and stackprot
Signed-off-by: Wayne Ren <wei.ren@synopsys.com>
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