V4L/DVB (4796): A couple of V4L2 defines needed by Cafe Camara driver

Two defines for V4L2, needed by the Cafe camera driver:
1) Add the RGB444 image format
2) Add the "init" internal command which is separate from "reset".

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>