ARM: dts: msm: Include smem reserved-mem region for sdxprairie

Split the peripheral2_mem region in the reserved-mem
region into tz_mem, smem_region and peripheral2_mem regions
inorder to have a separate reserved-mem region for smem on
sdxprairie.

Change-Id: I6e4b60a07440a7c8ee75b5c1b8d04deebc02dba7
Signed-off-by: Swathi Sridhar <swatsrid@codeaurora.org>