Add basic VLAN configuration

rtl837x_port.h

@@ -1,6 +1,9 @@
 #ifndef _RTL837X_PORT_H_
 #define _RTL837X_PORT_H_
 
+uint8_t port_l2_forget(void) __banked;
+void port_l2_learned(void) __banked;
 void port_stats_print(void) __banked;
+void vlan_setup(void) __banked;
 
 #endif