V4L/DVB (5268): Add support for three new MPEG controls.

Added V4L2_CID_MPEG_AUDIO_MUTE, V4L2_CID_MPEG_VIDEO_MUTE and
V4L2_CID_MPEG_CX2341X_STREAM_INSERT_NAV_PACKETS controls together with
their implementation in the cx2341x module.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>