defconfig: msm8916: enable strict memory protections

Enable STRICT_MEMORY_RWX for msm8916 defconfig so as to
restrict kernel memory permissions as much as possible.

Please note that it is kept disabled for 512MB based
defconfig for msm8916 as it has some memory overhead.

CRs-fixed: 648976
Change-Id: Ic983b5ad6a33c37eb11229ab9d5474f57a4dddf3
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>