Invoke a new device op 'device_feature' to handle just the data array
portion of the command. This lifts the ioctl validation to the core code
and makes it simpler for either the core code, or layered drivers, to
implement their own feature values.

Provide vfio_check_feature() to consolidate checking the flags/etc against
what the driver supports.

Link: https://lore.kernel.org/all/20220224142024.147653-9-yishaih@nvidia.comSigned-off-by: NJason Gunthorpe <jgg@nvidia.com>
Tested-by: NShameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Reviewed-by: NAlex Williamson <alex.williamson@redhat.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NYishai Hadas <yishaih@nvidia.com>
Signed-off-by: NLeon Romanovsky <leonro@nvidia.com>