V4L/DVB (11960): v4l: generate KEY_CAMERA instead of BTN_0 key events on input devices

A bunch of V4L drivers generate BTN_0 instead of KEY_CAMERA key presses.

X11 is able to handle KEY_CAMERA automatically these days while BTN_0 is
not treated at all.  Thus it would be of big benefit if the camera drivers
would consistently generate KEY_CAMERA.  Some drivers (uvc) already do,
this patch updates the remaining drivers to do the same.

I only possess a limited set of webcams, so this isn't tested with all
cameras.  The patch is rather trivial and compile tested, so I'd say it's
still good enough to get merged.

Signed-off-by: Lennart Poettering <mzxreary@0pointer.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>