media: cec-pin.h: move non-kAPI parts into cec-pin-priv.h

The kAPI cec-pin.h header also defined data structures that did
not belong here but were private to the CEC core code.

Split that part off into a cec-pin-priv.h header.

Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>