arm: mm: restrict kernel memory permissions if CONFIG_STRICT_MEMORY_RWX set

If CONFIG_STRICT_MEMORY_RWX is set, make kernel text RX,
kernel data/stack RW and rodata RO so that writing
on kernel text, executing kernel data or stack, or
writing on or executing read-only data is prohibited.

Change-Id: Ib2242c20dabddb63ef3f5655d5794fe418cb6287
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>
(cherry picked from commit 5a5305e90d4204fdf0586fbbd9a19b92181e74ea)

Conflicts:

	arch/arm/mm/mmu.c