drm/virtio: add define for second capset to the virgl code.

Although the kernel doesn't use this, qemu imports these headers
and it's best to keep them consistent.

This define is also something userspace may want to use.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180503021021.10694-1-airlied@gmail.com


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