msm: kgsl: Read the GMU firmware information once

Only read the GMU and HFI version information once. Once it is
read, subsequent starts will always use the same value. So store
the values locally and don't waste time reading them again.

Change-Id: Id2b5788342a502b2bdead0bbaaf957c420e9d608
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>