virgl: change vendor id to reflect reality more.

virgl vendor id should probably be little more generic now.

I think I picked this becuase the virtio pci id space was under
RH's name and they did pay for it, but at this point I think it's
better to just use something generic.

Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5483>

src/gallium/drivers/virgl/virgl_screen.c

@@ -54,7 +54,7 @@ DEBUG_GET_ONCE_FLAGS_OPTION(virgl_debug, "VIRGL_DEBUG", debug_options, 0)
 static const char *
 virgl_get_vendor(struct pipe_screen *screen)
 {
-   return "Red Hat";
+   return "Mesa/X.org";
 }