v3d/vc4: Remove primconvert from V3D and VC4 and re-enable PIPE_CAP_PRIMITIVE_RESTART for V3D.

Now that gallium handles primconvert this MR adds the configuration bits on the gallium capabilities for V3D and VC4. This was suggested at #5277

We are also re-enabling PIPE_CAP_PRIMITIVE_RESTART for V3D now that PIPE_CAP_EMULATE_NONFIXED_PRIMITIVE_RESTART gallium capability can be used when there are primitive restarts without fixed index. So we can enable NV_primitive_restart extension for OpenGL.