drm/msm/sde: update all qsync params in single commit

Update qsync params so that everything is set within the same
commit. Previously some settings may not get programmed until
one frame after the feature is enabled/disabled. This patch
also cleans up the qsync interface so that encoders no longer
directly access connector properties to get the qsync mode.

Change-Id: Icceb359ba13decac1c0faa5a974ffd9b4ccc8e95
Signed-off-by: Steve Cohen <cohens@codeaurora.org>
Signed-off-by: Abhijith Desai <desaia@codeaurora.org>