media: cec: core: add adap_unconfigured() callback

The adap_configured() callback was called with the adap->lock mutex
held if the 'configured' argument was false, and without the adap->lock
mutex held if that argument was true.

That was very confusing, and so split this up in a adap_unconfigured()
callback and a high-level configured() callback.

This also makes it easier to understand when the mutex is held: all
low-level adap_* callbacks are called with the mutex held. All other
callbacks are called without that mutex held.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Fixes: f1b57164 ("media: cec: add optional adap_configured callback")
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>