msm: kgsl: Halt GBIF before moving to NAP state

It has been observed that without gmu_clk, any active transactions will
cause that transaction to be stuck in QSMMU. As of now we don't halt
GBIF when moving to NAP state. So there is a possibility of transactions
inflight when gmu_clk is gated. This will cause transactions to be stuck
in QSMMU forever. This can eventually lead to GPU hang or TLB sync
timeout. So halt GBIF before moving to NAP.

Change-Id: I13bbe3b21b327d0d5c962bb2133c6d5d0f3a43c3
Signed-off-by: Puranam V G Tejaswi <pvgtejas@codeaurora.org>