ramips: provide label MAC address

This patch adds the label MAC address for several devices in
ramips.

Some devices require setting the MAC address in 02_network:

For the following devices, the netif device can be linked in
device tree, but the MAC address cannot be read:
- cudy,wr1000
- dlink,dir-615-d
- dlink,dir-615-h1
- dlink,dir-860l-b1
- glinet,gl-mt300a
- glinet,gl-mt300n
- glinet,gl-mt750
- vocore,vocore2
- vocore,vocore2-lite
- zbtlink,zbt-we1326
- zbtlink,zbt-wg3526

For the following devices, label MAC address is tied to lan or
wan, so no node to link to exists in device tree:
- dlink,dir-510l
- dlink,dwr-116-a1
- dlink,dwr-118-a1
- dlink,dwr-118-a2
- dlink,dwr-921-c1
- dlink,dwr-922-e2
- all hiwifi devices
- lava,lr-25g001
- xiaomi,mir3p

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ramips/dts/rt3050_dlink_dir-615-d.dts

@@ -14,6 +14,7 @@
 		led-failsafe = &led_status_green;
 		led-running = &led_status_green;
 		led-upgrade = &led_status_green;
+		label-mac-device = &wmac;
 	};
 
 	cfi@1f000000 {