V4L/DVB (9182): S2API: Added support for DTV_HIERARCHY

A user tuning DVB-T via the S2API reports that this was not implemented,
and his tuning was failing.

Signed-off-by: Steven Toth <stoth@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>