drm/msm/sde: update release fence handling for dp

On first commit for dp, encoder_mask of drm_crtc_state is zero
until the atomic check phase completes. So, this results in
incorrect release fence handling for dp. To fix this, check for
video mode capability for current commit from new_connector_state.

Change-Id: I7a129b942695d65c4df79de05771b048e3ce0c64
Signed-off-by: Jayaprakash <jmadiset@codeaurora.org>