media: cec/v4l2: move V4L2 specific CEC functions to V4L2

media: cec/v4l2: move V4L2 specific CEC functions to V4L2

Several CEC functions are actually specific for use with receivers,
i.e. they should be part of the V4L2 subsystem, not CEC.

These functions deal with validating and modifying EDIDs for (HDMI)
receivers, and they do not actually have anything to do with the CEC
subsystem and whether or not CEC is enabled. The problem was that if
the CEC_CORE config option was not set, then these functions would
become stubs, but that's not right: they should always be valid.

So replace the cec_ prefix by v4l2_ and move them to v4l2-dv-timings.c.
Update all drivers that call these accordingly.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: <stable@vger.kernel.org>      # for v4.17 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>