msm: kgsl: Fix IFPC abort due to preemption keepalive

Consider a scenario when preemption timer expires and while re-checking
preemption status in _a6xx_preemption_fault, if preemption is successful,
the state is transitioned to complete state. When dispatcher is scheduled,
it calls _a6xx_preemption_done. Here, we are not clearing preemption
keepalive bit which will prevent GMU to enter into IFPC state. Fix it by
clearing this bit. Similar situation can happen when we receive preempt
interrupt with non-zero status.

Change-Id: I7f2e5a139be766b363bc8d1941b1c6006e6a9ffd
Signed-off-by: Kamal Agrawal <kamaagra@codeaurora.org>