add void rt_hw_us_delay(rt_uint32_t us)

bsp/bluetrum/ab32vg1-ab-prougen/board/board.c

@@ -127,3 +127,8 @@ void rt_hw_board_init(void)
     rt_components_board_init();
 #endif
 }
+
+void rt_hw_us_delay(rt_uint32_t us)
+{
+
+}