media: imx: capture: Initialize video_device programmatically

Overwriting the whole video_device isn't future-proof as it would
overwrite any field initialized by video_device_alloc(). Furthermore,
the current implementation modifies the global template video_device as
if it were a per-instance structure, which is bad practice. To fix all
this, initialize the video device programmatically in
imx_media_capture_device_init().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>