V4L/DVB (13839): smsdvb: add ISDB-T as DVB-T tuning support hack

Activate ISDB-T mode using module option default_mode=6.

hack: use 4 lower bits in frequency for segment number

[mchehab@redhat.com: fix merge conflicts and CodingStyle]
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>