util: compile drm.o on posix

OpenGL isn't required to use DRM rendernodes. The following patches
uses it for 2d resources for ex.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20190524130946.31736-5-marcandre.lureau@redhat.com

[ kraxel s/LINUX/POSIX/ (fixes openbsd build failure) ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

util/Makefile.objs

@@ -53,7 +53,7 @@ util-obj-y += systemd.o
 util-obj-y += iova-tree.o
 util-obj-$(CONFIG_INOTIFY1) += filemonitor-inotify.o
 util-obj-$(CONFIG_LINUX) += vfio-helpers.o
-util-obj-$(CONFIG_OPENGL) += drm.o
+util-obj-$(CONFIG_POSIX) += drm.o
 util-obj-y += guest-random.o
 
 stub-obj-y += filemonitor-stub.o