V4L/DVB (8234): uvcvideo: Make input device support optional

UVC devices can report button events. The uvcvideo driver depends on
CONFIG_INPUT to report events to the input layer. This patch removes the hard
dependency by introducing a new CONFIG_USB_VIDEO_CLASS_INPUT_EVDEV option.

Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>