[media] Kconfig: merge all customise options into just one

Instead of having 3 options to allow customizing the media
sub-drivers (tuners, I2C drivers, frontends), merge all of
them into just one.

That simplifies the life for users, as they can just keep
this untouched.

Life for developers is also simpler, as there's now just
one Kconfig item to remember, for the ancillary sub-drivers
providing supports for chips that could change from one
board design to another.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>