Add a stub wl_drm implementation

This will allow us to remove all of our EGL wl_drm support code
and remove some weird stuff we need just for wl_drm support. In
particular, wl_drm buffers coming from the EGL implementation
can't easily be wrapped into a wlr_buffer properly.

include/wlr/types/wlr_drm.h

@@ -0,0 +1,36 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
+#ifndef WLR_TYPES_WLR_DRM_H
+#define WLR_TYPES_WLR_DRM_H
+
+#include <wayland-server-protocol.h>
+
+struct wlr_renderer;
+
+/**
+ * A stub implementation of Mesa's wl_drm protocol.
+ *
+ * It only implements the minimum necessary for modern clients to behave
+ * properly. In particular, flink handles are left unimplemented.
+ */
+struct wlr_drm {
+	struct wl_global *global;
+	char *node_name;
+
+	struct {
+		struct wl_signal destroy;
+	} events;
+
+	struct wl_listener display_destroy;
+};
+
+struct wlr_drm *wlr_drm_create(struct wl_display *display,
+	struct wlr_renderer *renderer);
+
+#endif