compositor: pass the backend config struct to the backends init function

Add new configuration argument to the backend_init() function, which
will replace the current argc, argv, and config arguments.
After each backend is converted individually the unused parameters
will be removed.

Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
diff --git a/src/compositor-wayland.c b/src/compositor-wayland.c
index 7b11ae4..a819867 100644
--- a/src/compositor-wayland.c
+++ b/src/compositor-wayland.c
@@ -2056,7 +2056,8 @@
 
 WL_EXPORT int
 backend_init(struct weston_compositor *compositor, int *argc, char *argv[],
-	     struct weston_config *config)
+	     struct weston_config *config,
+	     struct weston_backend_config *config_base)
 {
 	struct wayland_backend *b;
 	struct wayland_output *output;