V4L/DVB (10211): vivi: Implements 4 inputs on vivi

This patch adds the capability of selecting between 4 different inputs
on vivi driver. Input 0 is the normal color bar, while inputs 1-3 are
modified color bars.

This allows testing input selection on userspace applications and
serves as an implementation model for other drivers.

The current approach allows a maximum of 10 different inputs, since the
input name generator assumes that we need just one digit to present the
input. It shouldn't be hard to modify it to present a bigger name of
inputs, but, in fact, it doesn't make much sense of doing it for this
test driver.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>