msm: kgsl: refcount irq to avoid racing against idle check

Current irq handler clears the pending interrupt bits in interrupt
status register before serving the interrupts. This leads to a race
condition with the idle check which checks the interrupt status
register to determine whether any interrupt is pending or not. As
the interrupt status register is already cleared, idle check goes
ahead and switch off the GPU clocks even when irq is yet to be served
causing NOC errors.

This change refcounts each irq handler call and uses this reference
count to determine if any irq is still pending or not along with
interrupt status register to avoid this race condition.

Change-Id: I030d52c52055f836ea4c7519ce2d8db94a2a09a0
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>