ARM: dts: msm: Add memory hole for msm8926

Add the start address and size of the memory regions
reserved for other images. As the device tree for msm8926
is derived from the device tree for msm8226 add a tag to
the memory hole node to support the different memory map
configurations

Change-Id: I7885d5fb143cc59b7691b7f5dc24b79caee598a6
Signed-off-by: Neeti Desai <neetid@codeaurora.org>