defconfig: msm8909: Optimize memory configuration

Disable STRICT_MEMORY_RWX and DYNAMIC_DEBUG for 512
MB perf defconfig as both these configs have memory
overhead while we keep it enabled in 512 MB defconfig
and on 1 GB targets.

Reduce common CMA area to 8 MB for both 1 GB as
well as 512 MB targets because as per last
profiling usage of common CMA areas was
just over 4 MB. So now even if memory requirement
are increasing by 1 MB to 2 MB we would have sufficient
buffer to accomodate the requirement.

Change-Id: I097450c44a5a57a14b3b6000cfb2f6cf7add6dd5
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>