V4L/DVB: vivi: clean up and a major overhaul

V4L/DVB: vivi: clean up and a major overhaul

- Clean up the code
- Use the kernel's built-in vga8x16 font instead of our own.
- Drop exclusive open: now multiple users can open the device as per the V4L2 spec.
- Move the format description to the vivi device instead of keeping it in the file
  handle. Again as per the spec.
- Streamline and simplify the drawing code. It is now easy to add text on top of
  the colorbar pattern.
- Upgrade the max resolution to 1920x1200.

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