[media] DVB: dib0700, separate stk7070pd initialization

The start is common for both stk7070pd and novatd specific routine.
This is just a preparation for the next patch.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Patrick Boettcher <pboettcher@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>