[media] V4L spec: fix typo and missing CAP_RDS documentation

For some reason the V4L2_TUNER_CAP_RDS_CONTROLS/BLOCK_IO capabilities were never
documented in the proper table. In addition, then RDS interface section incorrectly
referred to them as V4L2_TUNER_SUB_RDS_... instead of CAP_RDS_...

This is now fixed.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>