media: v4l: Add support for STD ioctls on subdev nodes

There is no way to control the standard of subdevices which are part of
a media device. The ioctls which exists all target video devices
explicitly and the idea is that the video device should talk to the
subdevice. For subdevices part of a media graph this is not possible and
the standard must be controlled on the subdev device directly.

Add four new ioctls to be able to directly interact with subdevices and
control the video standard; VIDIOC_SUBDEV_ENUMSTD, VIDIOC_SUBDEV_G_STD,
VIDIOC_SUBDEV_S_STD and VIDIOC_SUBDEV_QUERYSTD.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>