virglrendnerer should only report compute capabilities when the host OpenGL is at least 3.3
We require GLSL 330 when compute shaders are created on a GL context, but we might report compute shaders also when the host reports ARB_compute_shaders, but has only OpenGL 3.2.
It might be a bug in mesa to actually allow the latter (i.e. ARB_compute_shader says "OpenGL 4.2 required), but we should protect against this too.