V4L/DVB: media: dvb/af9015, factor out remote setting

This is just a code shuffle without functional changes. For easier
review of later changes, i.e. preparation.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>