virgl/drm: explicit context initialization
If the host supports explicit context initialization, try it. If no capabilitiies associated with virgl are present, return an error. Reviewed-by:Anthoine Bourgeois <anthoine.bourgeois@gmail.com> Tested-by:
Anthoine Bourgeois <anthoine.bourgeois@gmail.com> Part-of: <mesa/mesa!7712>