allocator: remove backend parameter in allocator_autocreate_with_drm_fd

Since we only use the backend capabilities here we can simply pass
them in directly. This allows other locations to create an allocator
even if they don't have a backend. They can simply specify the caps
they want instead.

backend/drm/renderer.c

@@ -6,6 +6,7 @@
 #include "backend/drm/drm.h"
 #include "backend/drm/fb.h"
 #include "backend/drm/renderer.h"
+#include "backend/backend.h"
 #include "render/drm_format_set.h"
 #include "render/allocator/allocator.h"
 #include "render/pixel_format.h"
@@ -19,7 +20,8 @@ bool init_drm_renderer(struct wlr_drm_backend *drm,
 		return false;
 	}
 
-	renderer->allocator = allocator_autocreate_with_drm_fd(&drm->backend,
+	uint32_t backend_caps = backend_get_buffer_caps(&drm->backend);
+	renderer->allocator = allocator_autocreate_with_drm_fd(backend_caps,
 		renderer->wlr_rend, drm->fd);
 	if (renderer->allocator == NULL) {
 		wlr_log(WLR_ERROR, "Failed to create allocator");

include/render/allocator/allocator.h

@@ -4,6 +4,6 @@
 #include <wlr/render/allocator.h>
 
 struct wlr_allocator *allocator_autocreate_with_drm_fd(
-	struct wlr_backend *backend, struct wlr_renderer *renderer, int drm_fd);
+	uint32_t backend_caps, struct wlr_renderer *renderer, int drm_fd);
 
 #endif

render/allocator/allocator.c

@@ -93,9 +93,8 @@ static int reopen_drm_node(int drm_fd, bool allow_render_node) {
 }
 
 struct wlr_allocator *allocator_autocreate_with_drm_fd(
-		struct wlr_backend *backend, struct wlr_renderer *renderer,
+		uint32_t backend_caps, struct wlr_renderer *renderer,
 		int drm_fd) {
-	uint32_t backend_caps = backend_get_buffer_caps(backend);
 	uint32_t renderer_caps = renderer_get_render_buffer_caps(renderer);
 
 	struct wlr_allocator *alloc = NULL;
@@ -149,12 +148,14 @@ struct wlr_allocator *allocator_autocreate_with_drm_fd(
 
 struct wlr_allocator *wlr_allocator_autocreate(struct wlr_backend *backend,
 		struct wlr_renderer *renderer) {
+	uint32_t backend_caps = backend_get_buffer_caps(backend);
 	// Note, drm_fd may be negative if unavailable
 	int drm_fd = wlr_backend_get_drm_fd(backend);
 	if (drm_fd < 0) {
 		drm_fd = wlr_renderer_get_drm_fd(renderer);
 	}
-	return allocator_autocreate_with_drm_fd(backend, renderer, drm_fd);
+
+	return allocator_autocreate_with_drm_fd(backend_caps, renderer, drm_fd);
 }
 
 void wlr_allocator_destroy(struct wlr_allocator *alloc) {