device: support generating defines from devicetree nodes with no label

The existing code only worked for nodes that had a label property,
which is every device except ESP32 pinmux.  However, a label property
should not be necessary for defining a device from devicetree.

Signed-off-by: Peter Bigot <[email protected]>

Author: pabigot

include/device.h

@@ -168,7 +168,8 @@ extern "C" {
  */
 #define DEVICE_DT_DEFINE(node_id, init_fn, pm_control_fn,		\
 			 data_ptr, cfg_ptr, level, prio, api_ptr)	\
-	Z_DEVICE_DEFINE(node_id, node_id, DT_LABEL(node_id), init_fn,	\
+	Z_DEVICE_DEFINE(node_id, node_id,				\
+			DT_PROP_OR(node_id, label, NULL), init_fn,	\
 			pm_control_fn,					\
 			data_ptr, cfg_ptr, level, prio, api_ptr)