[media] bw-qcam: driver and pixfmt documentation fixes

Fix the documentation of the Y4 and Y6 formats.
Fix a poll() issue, add support for enum_frmsizes, set the proper
parent device and fix a few compliance issues.

Tested with an actual Connectix B&W parallel port webcam, both on a
little-endian and a big-endian platform. This driver has never been
so good, doing 320x240 at 1 frame per second :-)

I know, nobody cares, but still it is cool that linux can still support
this old webcam.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>