msm: kgsl: Avoid race with Fence Drop mode in Preemption trigger

Even with preemption keepalive bit set, accessing fenced registers
can race with GMU moving to Fence Drop mode. It is safer to use
fenced write for these registers. Also handle a fence write failure
with GMU recovery.

Change-Id: I4677be0e16b2881b69e87591cf3ef78286316ae9
Signed-off-by: Akhil P Oommen <akhilpo@codeaurora.org>