ARM: dts: msm: Align splash memory size to 4MB

As splash memory is allocated from CMA heap, memory reservation size
is aligned to 4MB where as memblock_free is freeing only requested size
resulting in part of memory being always marked as reserved. Fix this by
requesting for size aligned to 4MB.

Change-Id: I763f07efff5cc55992149a3ef9133cfbbc9a54a8
Signed-off-by: Vishnuvardhan Prodduturi <vproddut@codeaurora.org>