drm/msm/dsi-staging: add qsync/avr support in dsi controller

Control the AVR_SUPPORT_ENABLE bit in the VIDEO_MODE_CTRL register
when qsync video mode is enabled/disabled.

Change-Id: I451cceec30397b9a75791edb450b6f992da6d746
Signed-off-by: Steve Cohen <cohens@codeaurora.org>