drm/msm/sde: update auto-refresh disable during cont-spalsh

Continuous splash feature disables the auto-refresh and
waits for pp_done IRQ before attaching SMMU context bank.
Current logic clears this pp_done IRQ before disabling
the auto-refresh on pingppong. There could be a race
condition between in this operation with HW vsync. New
autorefresh disable sequence will turn off the HW vsync
and executes the disable sequence. It also avoids reading
stale pp_done IRQ by resetting the IRQ after autorefresh
done on pingpong.

Change-Id: I16b61e9248f1c5121ea36a25972b2d9d75c094ac
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>