net: lwm2m: implement utc_offset and timezone

Implemented UTC_OFFSET and TIMEZONE to device.

Signed-off-by: Martin Lesund <martin.lesund@nordicsemi.no>
diff --git a/subsys/net/lib/lwm2m/lwm2m_obj_device.c b/subsys/net/lib/lwm2m/lwm2m_obj_device.c
index acc3154..57ffd3d 100644
--- a/subsys/net/lib/lwm2m/lwm2m_obj_device.c
+++ b/subsys/net/lib/lwm2m/lwm2m_obj_device.c
@@ -7,7 +7,6 @@
 
 /*
  * TODO:
- * - Implement UTC_OFFSET & TIMEZONE
  * - Configurable CURRENT_TIME notification delay
  */
 
@@ -330,6 +329,8 @@
 			 current_time_read_cb,
 			 current_time_pre_write_cb,
 			 current_time_post_write_cb, NULL);
+	INIT_OBJ_RES_OPTDATA(DEVICE_UTC_OFFSET_ID, res, i, res_inst, j);
+	INIT_OBJ_RES_OPTDATA(DEVICE_TIMEZONE_ID, res, i, res_inst, j);
 	INIT_OBJ_RES_DATA(DEVICE_SUPPORTED_BINDING_MODES_ID, res, i,
 			  res_inst, j, binding_mode, DEVICE_STRING_SHORT);
 	INIT_OBJ_RES_OPTDATA(DEVICE_TYPE_ID, res, i, res_inst, j);