[media] DocBook media: Cleanup some sections at common.xml

Updates sections "Querying Capabilities", "Application Priority",
"Video Inputs and Outputs" and "Audio Inputs and Outputs".

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>