drm/msm/sde: ensure qsync settings are properly flushed

Ensure the correct block is flushed when QSYNC settings are
updated.  Depending on the HW version, the location of the
Tear Effect module, and the interface mode, either the layer
mixer or the interface must be flushed when QSYNC settings
are changed.

Change-Id: I89b654ec03cbb5df459918a1b9ab345fe5a756ea
Signed-off-by: Steve Cohen <cohens@codeaurora.org>