glamor: Use render node for glamor device path where possible

On certain system deployments, /dev/dri/card* nodes aren't directly accessible to the currently logged in user, but the display server only access it by asking systemd-logind to open the device for it. This causes the X server to fail when trying to re-open the card* device directly, causing all use of DRI3 to fail.

Fix this by using the render device path instead where possible.