msm: kgsl: Fix the maximum number of allowable memory types

The memtype field in the memory flags allows for 3 bits for
the memory type.  Even though we only define 4 types now we
need to account for the other 4 in case they start getting
used.

Change-Id: Ic0dedbadeb644614935f48145ebf5e73d3c603f3
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>