OMAPDSS: APPLY: add busy field to mgr_priv_data

Add a new field to mgr_priv data, "busy", which is used to track the
status of GO bit with the manager. As manual update displays never use
the GO bit, the field is always false for managers used for manual
update displays.

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