Adds more osd mode switching information.
Corrects some information regarding mode selection & local alpha operation for
16 bit modes.
Signed-off-by: NIan Armstrong <ian@iarmst.demon.co.uk>
Signed-off-by: NHans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>