media: stkwebcam: deprecate driver, move to staging

This is a very old driver for very old hardware and it is one of
the very few remaining that does not use the vb2 framework (or
even the older videobuf framework), so deprecate this driver
and move it to staging with the intent to removing it altogether
by the end of 2022.

If someone wants to keep this driver, then it has to be converted
to use vb2.

Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>