[media] v4l2_subdev: describe ioctl parms at the remaining structs

Fixes the following warnings:

Warning(.//include/media/v4l2-subdev.h:445): No description found for parameter 'g_sliced_vbi_cap'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'enum_mbus_code'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'enum_frame_size'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'enum_frame_interval'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'get_fmt'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'set_fmt'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'get_selection'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'set_selection'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'get_edid'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'set_edid'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'dv_timings_cap'
Warning(.//include/media/v4l2-subdev.h:589): No description found for parameter 'enum_dv_timings'

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>