[media] media: au0828-core register entity_notify hook

Register entity_notify async hook to create links between existing
bridge driver entities and a newly added non-bridge driver entities. For
example, this handler creates link between V4L decoder entity and ALSA
mixer entity.

[mchehab@osg.samsung.com: fix merge conflicts and make
 au0828_media_graph_notify static to shut up a warning]

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>