[media] v4l: Add VIDIOC_LOG_STATUS support for sub-device nodes

The VIDIOC_LOG_STATUS ioctl allows to dump the current status of a driver
to the kernel log. Currently this ioctl is only available at video device
nodes and the subdevs rely on the host driver to expose their core.log_status
operation to user space.

This patch adds VIDIOC_LOG_STATUS support at the sub-device nodes,
for standalone subdevs that expose their own /dev entry.

Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>