media: Kconfig: DVB support should be enabled for Digital TV

As we reverted changeset 85f7cd3a ("Revert "media: Kconfig: better support hybrid TV devices""),
we should add a default to DVB_CORE, as otherwise DVB support won't work.

Fixes: 85f7cd3a ("Revert "media: Kconfig: better support hybrid TV devices"")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>