util: promote qemu_egl_rendernode_open() to libqemuutil

vhost-user-gpu will share the same code to open a DRM node.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180713130916.4153-20-marcandre.lureau@redhat.com>

[ kraxel: buildfix: util/drm.o must be CONFIG_OPENGL not CONFIG_LINUX ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 6902a56..282d6a8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1566,6 +1566,7 @@
 F: ui/
 F: include/ui/
 F: qapi/ui.json
+F: util/drm.c
 
 Cocoa graphics
 M: Peter Maydell <peter.maydell@linaro.org>