media: via-camera: fix v4l2-compliance fails

The patch fixes various v4l2-compliance failures:

- missing support for control events
- support of s/g_std even though this doesn't apply to a webcam
- missing colorspace reporting
- bus_info wasn't filled in by VIDIOC_QUERYCAP
- parm.capture.readbuffers was overridden with wrong value
- viacam_enum_framesizes/intervals didn't check the arguments

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>