arm/src/common/mpu_init.c: Fix max MPU region issue
arm/src/common/mpu_init.c: Fix max MPU region issue

When common binary is enabled, then more mpu regions are used, in this
case, we are getting assert failure during mpu_init since we are using
max mpu regions (rtk regions, common binary regions, app regions, stack region).
The g_mpu_region_usages.max_nregion variable indicates the total number
mpu regions being used. Its value can be 0 if no region is used, and max (8)
if all regions are used. So, we change the assert statement accordingly.

Signed-off-by: Abhishek Akkabathula <d7e0068fa4fa5deac598bc54a95fdd440f7851ef@samsung.com>

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