virgl: Add a caps feature check version
When we add new feature checks on the host side that is used to enable a cap conditionally that was enabled unconditionally before we might end up with a feature regression when a new mesa version is used with an old virglrenderer version that doesn't check for that cap.
To work around this problem add a version id to the caps that corresponds to the features that are actually checked on the host and check that version too when enabling the cap.
Fixes: 2ee197d6 virgl: Enable mixed color FBO attachemnets only when the host supports it
The virglrenderer side is here: virgl/virglrenderer!205 (merged)