media: rename MEDIA_ENT_F_DTV_DECODER to MEDIA_ENT_F_DV_DECODER

The use of 'DTV' is very confusing since it normally refers to Digital
TV e.g. DVB etc.

Instead use 'DV' (Digital Video), which nicely corresponds to the
DV Timings API used to configure such receivers and transmitters.

We keep an alias to avoid breaking userspace applications.

Since this alias is only available if __KERNEL__ is *not* defined
(i.e. it is only available for userspace, not kernelspace), any
drivers that use it also have to be converted to the new define.
These drivers are adv7604, adv7842 and tda1997x.

Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>