V4L/DVB (6879): move struct analog_tuner_ops into dvb_frontend.h

struct analog_tuner_ops no longer has any dependencies specific
to v4l2, so we can move this into dvb_frontend.h with the rest
of the tuning structures.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>