media: iris: implement iris v4l2 file ops

Implement open, close and poll ops.

Open:
Configure the vb2 queue and v4l2 file handler. Allocate a video instance
and add the instance to core instance list.

Close:
Free the instance and remove it from core instance list.

Poll:
Wait for an event on vb2 src and vb2 dst queues.

Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>
Tested-by: Stefan Schmidt <stefan.schmidt@linaro.org> # x1e80100 (Dell XPS 13 9345)
Reviewed-by: Stefan Schmidt <stefan.schmidt@linaro.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-HDK
Signed-off-by: Dikshita Agarwal <quic_dikshita@quicinc.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>