drm: Add acquire ctx parameter to ->update_plane

Just rolling it out, no code change here.

Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Eric Anholt <eric@anholt.net>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170322215058.8671-3-daniel.vetter@ffwll.ch