media: ipu6: Rework CSI-2 sub-device streaming control

CSI-2 sub-device streaming control should use {enable,disable}_streams pad
ops and not s_stream video ops as the sub-device supports streams. Fix
this by removing driver-implemented stream management and moving sensor
streaming control to the CSI-2 sub-device sub-driver.

Fixes: a11a5570 ("media: intel/ipu6: add IPU6 CSI2 receiver v4l2 sub-device")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>