[media] v4l: add enum_freq_bands support to tuner sub-device

Add VIDIOC_ENUM_FREQ_BANDS, enumerate supported frequency bands,
IOCTL support for sub-device tuners too.

Cc: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: NAntti Palosaari <crope@iki.fi>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

include/media/v4l2-subdev.h

@@ -196,6 +196,7 @@ struct v4l2_subdev_tuner_ops {
 	int (*s_radio)(struct v4l2_subdev *sd);
 	int (*s_frequency)(struct v4l2_subdev *sd, const struct v4l2_frequency *freq);
 	int (*g_frequency)(struct v4l2_subdev *sd, struct v4l2_frequency *freq);
+	int (*enum_freq_bands)(struct v4l2_subdev *sd, struct v4l2_frequency_band *band);
 	int (*g_tuner)(struct v4l2_subdev *sd, struct v4l2_tuner *vt);
 	int (*s_tuner)(struct v4l2_subdev *sd, const struct v4l2_tuner *vt);
 	int (*g_modulator)(struct v4l2_subdev *sd, struct v4l2_modulator *vm);