Move allocator stuff into new directory

Add render/allocator/ and include/render/allocator/ to hold
everything allocator-related.

include/render/allocator/gbm.h

@@ -0,0 +1,34 @@
+#ifndef RENDER_ALLOCATOR_GBM_H
+#define RENDER_ALLOCATOR_GBM_H
+
+#include <gbm.h>
+#include <wlr/render/dmabuf.h>
+#include <wlr/types/wlr_buffer.h>
+#include "render/allocator/allocator.h"
+
+struct wlr_gbm_buffer {
+	struct wlr_buffer base;
+
+	struct wl_list link; // wlr_gbm_allocator.buffers
+
+	struct gbm_bo *gbm_bo; // NULL if the gbm_device has been destroyed
+	struct wlr_dmabuf_attributes dmabuf;
+};
+
+struct wlr_gbm_allocator {
+	struct wlr_allocator base;
+
+	int fd;
+	struct gbm_device *gbm_device;
+
+	struct wl_list buffers; // wlr_gbm_buffer.link
+};
+
+/**
+ * Creates a new GBM allocator from a DRM FD.
+ *
+ * Does not take ownership over the FD.
+ */
+struct wlr_allocator *wlr_gbm_allocator_create(int drm_fd);
+
+#endif