msm: kgsl: Halt RGMU execution before dumping snapshot

On GPU and GMU soft fault detection there is possibility
of putting GX in OFF state during the snapshot dump path.
Ensure that RGMU is halted before dump the snapshot to
avoid getting stale data from the GX registers.

Also add some additional debug register dumps to
analyze rgmu_wait_for_lowest_idle() failure.

Change-Id: I04223a1bc566c6bd960ae4141506fbddfbd59533
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>