drm/virtio: kms: use drm managed resources

Allocate driver structures with drm managed resource allocators in order
to cleanup/simplify the drm driver .release callback.

Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20220714130028.2127858-3-dakr@redhat.com


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>