drm/msm/sde: add sde_connector kickoff callbacks

Add a callback into the connector framework to allow sending
per-frame parameters at kickoff time.

This is needed to support the HDR feature where the HDR
metadata shall be sent to the sink on a per-frame basis.

Change-Id: I48a3616509e2226ea9bf0f490f0f47873ca74781
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>