msm: kgsl: clear GMU flags before hibernation

Clear GMU_BOOT_INIT_DONE and GMU_RSCC_SLEEP_SEQ_DONE bits
in gmu_core flags before hibernation, to force GMU power
up sequence after resuming.

Change-Id: I02a2d25dbb7dec2f9b06a8e6857326e8b40f62da
Signed-off-by: Kasin Li <donglil@codeaurora.org>
Signed-off-by: Thomas (Wonyoung) Yun <wyun@codeaurora.org>