drm/i915: wait for all DSI FIFOs to be empty

Ensure that the DSI packets for a particular sequence are completely
sent before going ahead in the enabling or disabling of the panel

Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/intel_dsi.c
Simple merge

diff --cc drivers/gpu/drm/i915/intel_dsi_cmd.c
Simple merge

diff --cc drivers/gpu/drm/i915/intel_dsi_cmd.h
Simple merge