[media] media: Move au8522_media_pads enum to au8522.h from au8522_priv.h

Move the au8522_media_pads enum to au8522.h from au8522_priv.h to export
them. This will allow au0828-core to use these defines instead of
hard-coding them them.

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