ARM: dts: msm: Add memory map for 512MB msm8916 platforms

In order to reduce memory usage on low memory (512MB)
msm8916 platforms, new and optimized memory map is required.

Refactor and remove the memory layout from common
msm8916.dtsi in to separate files for generic and low memory
platforms. Subsequently let individual platforms choose the
right memory layout for them.

CRs-fixed: 639052
Change-Id: I128bac03c21690d35e58e1947ce1e8fc54f20352
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>