FROMLIST: media: Kconfig: Fix DVB_CORE can't be selected as module

The DVB_CORE now depends on MEDIA_DIGITAL_TV_SUPPORT and
default MEDIA_DIGITAL_TV_SUPPORT, and this makes it can never be =m
since the type of MEDIA_DIGITAL_TV_SUPPORT is bool.

Change MEDIA_DIGITAL_TV_SUPPORT to tristate so it's possible to set
DVB_CORE as =m.

Link: https://lore.kernel.org/lkml/20210608101451.9301-1-lecopzer.chen@mediatek.com/


Bug: 189516917
Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Change-Id: I3e62e9f6b0e3e42b3ce8b7d179266700bb25e6a0