msm: kgsl: check kgsl state before accessing device registers

In some unfortunate scenarios it is possible that dispatcher is
scheduled when kgsl state is not awake. Consider the scenario
when GMU stop failed. During subsequent wake, GMU boot failed and
watchdog interrupt has been received. In the handler GPU fault is
set and dipatcher_do_fault() is triggered. Here device registers
are accessed and kgsl state is slumber as previous wake failed.
So check kgsl state before accessing any register.

Change-Id: Ibbc2366e34d3351af997dcd68f7e749ef2869e55
Signed-off-by: Puranam V G Tejaswi <pvgtejas@codeaurora.org>