New now ask Glamor to use EGL_MESA_query_driver to obtain the DRI driver
name; if successful, we use that as the DRI driver name.  Since this is
a generic GL-based video driver, we also pair it with the "va_gl" VDPAU
driver.

This allows us to bypass the PCI ID lists in xserver and centralize the
driver selection mechanism inside Mesa.  The hope is that we no longer
have to update these lists for any future hardware.