drm/virtio: implement context init: track valid capabilities in a mask

drm/virtio: implement context init: track valid capabilities in a mask

The valid capability IDs are between 1 to 63, and defined in the
virtio gpu spec.  This is used for error checking the subsequent
patches.  We're currently only using 2 capability IDs, so this
should be plenty for the immediate future.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Lingfeng Yang <lfy@google.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210921232024.817-4-gurchetansingh@chromium.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>