msm: kgsl: Fix stall on pagefault sequence

As we do not clear FSR in the GPU fault handler,
we have to disable context fault interrupts until
the FSR is cleared. Not doing so results in the
interrupt firing multiple times for the same pagefault.
Fix the CP CACHE_FLUSH_TS interrupt storm by inserting
a WAIT_MEM_WRITES packet just before the EVENT_WRITE -
CACHE_FLUSH_TS. This ensures that all preceding memory
writes have completed.
Also, set the default pagetable for the context else
some functions will return early doing nothing.

Change-Id: Ifdfe10de7b52053560209692b3340a3b300281a2
Signed-off-by: Sushmita Susheelendra <ssusheel@codeaurora.org>