media: imx: imx7-media-csi: Merge streaming_start() with csi_enable()

The imx7_csi_streaming_start() function just wraps imx7_csi_enable().
Call the latter directly.

Similarly, merge imx7_csi_streaming_stop() and imx7_csi_disable() as
they're both called from a single location only.

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