[media] media: Media Controller export non locking __media_entity_setup_link()

Export __media_entity_setup_link() to be used from code paths
that hold the graph_mutex.

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