msm: kgsl: Force VA alignment and padding if required

Some targets require all GPU virtual mappings to be aligned to and
padded up to a particular size. Allocate a padding page and map it
into the virtual space as many times as necessary to make up the size
required by the target.

Change-Id: I8f41c83bf88c20cf619ce2a7a63c31a05b732c4d
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>