[media] V4L2: Add seek spacing and RDS CAP bits

Add spacing field to v4l2_hw_freq_seek.

Add V4L2_TUNER_CAP_RDS_BLOCK_IO, which indicates that the tuner/
transmitter if capable of transmitting/receiving RDS blocks.

Add V4L2_TUNER_CAP_RDS_CONTROLS capability, which indicates that the
RDS data is handled as values of predefined controls like radio text,
program ID and so on.

Signed-off-by: Matti J. Aaltonen <matti.j.aaltonen@nokia.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>