V4L/DVB (3518): Creates a virtual video device driver

The Virtual Video Device Driver (aka vivi) is a device that
can be used to:
	1) test core v4l functionalities;
	2) be a prototype for newer development.
Vivi were developed using the best practices for v4l driver. 
When loaded, it provides a video device that generates a
standard color bar, with a timestamp placed at top left corner.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>