vfio/gvt: Use mdev_get_type_group_id()

intel_gvt_init_vgpu_type_groups() makes gvt->types 1:1 with the
supported_type_groups array, so the type_group_id is also the index into
gvt->types. Use it directly and remove the string matching.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Message-Id: <16-v2-d36939638fc6+d54-vfio2_jgg@nvidia.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>