kvm/vfio: Move KVM_DEV_VFIO_GROUP_* ioctls into functions

To make it easier to read and change in following patches.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/1-v3-f7729924a7ea+25e33-vfio_kvm_no_group_jgg@nvidia.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>