drm/omap: add writeback funcs to dispc_ops

Add writeback specific dispc functions to dispc_ops so that omapdrm can
use them.  Also move 'enum dss_writeback_channel' to the public
omapdss.h for omapdrm.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
3 files changed