output: Turn winsys_id into a uint64_t

We need a 64 bit field to combine the device id and connector
id into the output id (winsys_id).

src/backends/meta-output.h

@@ -66,7 +66,7 @@ struct _MetaOutput
   MetaGpu *gpu;
 
   /* The low-level ID of this output, used to apply back configuration */
-  glong winsys_id;
+  uint64_t winsys_id;
   char *name;
   char *vendor;
   char *product;