[1.20 backport] modesetting: Use EGL_MESA_query_driver where available to choose the DRI driver
Here is a backport of !351 (merged) to server-1.20-branch. I'd like to include it there so that people can use the new iris driver for Glamor acceleration without upgrading to xserver master. It would also help people trying to use Tigerlake support, which requires iris.