msm: kgsl: Wait longer for CX GDSC going off

Avoids false alarm due to kernel preemption latency. Longer timeout
allows GMU watchdog timer to alarm on GMU hang. Watchdog timeout
interrupt could provide more accurate GMU debugging information.

Change-Id: I50dd50089bebc61a3db8c2b635c534b356809eef
Signed-off-by: George Shen <sqiao@codeaurora.org>