ARM: dts: msm: add mem dump entry to imem device node for 8916

This will provide memory dump imem base and size info that will
be used by the memory dump v2 driver to create a mapping. Driver
will populate it with the physical address of the memory dump
base table address.

Change-Id: I9a12b6b19eb47a00a3ae4817396113791bd6a68a
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>