V4L/DVB (12379): uvcvideo: Multiple streaming interfaces support

Restructure the UVC descriptors parsing code to handle multiple streaming
interfaces. The driver now creates a uvc_video_chain instance for each chain
detected in the UVC control interface descriptors, and tries to register one
video device per streaming endpoint.

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