drm/i915/dsb: Allow vblank synchronized DSB execution

Allow the caller to ask for the DSB commands to execute
during vblank.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230118163040.29808-7-ville.syrjala@linux.intel.com


Reviewed-by: Animesh Manna <animesh.manna@intel.com>