disp: msm: sde: update RSC when QSYNC property is updated

RSC is updated during encoder enable/disable/modeset or power-
collapse/wakeup. The RSC vote for primary display will change
depending on QSYNC status which might change without modeset or
power-collapse. Add a call to update the primary display's vote
when the QSYNC property is updated.

Change-Id: I664754e4aae689ef2db5b1ef7b8b55a4c5fad3be
Signed-off-by: Steve Cohen <cohens@codeaurora.org>