msm: kgsl: Allow compatible string matching for gpu devices

Allow a GPU definition to specify a compatible string to match a GPU
target. If specified a matching compatible string will take priority
over the GPU chipid match.

Change-Id: Ic0dedbadd998dcc8e8f9bc5de2e383870258ad48
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>