msm: simplify placing memory pools

The algorithm for placing memory pools was manually inspecting
the memblock data structures and then doing a memblock_remove()
on the region it decided that the memory pool should be located at.

If other code already did a memblock_remove() it was possible
that the memblock data structures which this algorithm
was inspecting would not be correct and the memory pool might
be placed overlapping this previous allocation.

Instead use arm_memblock_steal() which will not have this
problem (and also lets the memblock subsystem do
the allocation without any manual inspection of memblocks).

Change-Id: I7db5cba0a8d5f222f9f2f131b4b42eb81171c45b
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>