media: cadence: csi2rx: Add enum_mbus_code pad ops

Add enum_mbus_code ioctl so that user space can know what
formats are supported to csi2rx.

Signed-off-by: Changhuang Liang <changhuang.liang@starfivetech.com>
Reviewed-by: Julien Massot <julien.massot@collabora.com>
Tested-by: Julien Massot <julien.massot@collabora.com>
Reviewed-by: Jai Luthra <j-luthra@ti.com>
Tested-by: Jai Luthra <j-luthra@ti.com> # [Test on sk-am62a]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>