V4L/DVB (3700): Remove obsolete commands from tvp5150.c

- Remove old DECODER_ commands from tvp5150.c, replacing them with newer
  ones if appropriate.
- Small VIDIOC_G_TUNER fixes in msp3400 and tuner.
- Fix VIDIOC_S_TUNER support in em28xx.

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