msm: kgsl: Allow GMU preallocation requests

Allow the GMU firmware to make GMU address assignments before
KGSL is allowed to allocate from the GMU address space.

Change-Id: I0e2b4f3cd5a7f993f09338b7756eaeb4050a06ff
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>