msm: kgsl: Restrict allocated memory alignment to a max of 2^31

The GPU memory allocation flags allow 8 bits of space to specify
a power of 2 aligment for the allocated memory block.  Cap the
actual alignment to 2^31 since any value more than that will have
unintended effects on a 32 bit system.

Change-Id: Ic0dedbadd42a9a886b8bfada0c7d415caaed65de
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>