msm: allow memory pools to be created from multiple memory banks

On platforms which require very large memory pools, it
might not be possible to create such a memory pool from
a single memory bank (even though there may be several
contiguous memory banks of the same memory type), and
the memory pool created would then be smaller than requested.

Allow multiple contiguous memory banks to be used in the
creation of memory pools, making it more likely that a
large memory pool can be created of the desired size.

Change-Id: Ie955f65a7412d18f01e7e93d8d039318ff70b66b
CRs-Fixed: 333361
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>