ramips: add support for TP-Link TL-MR3420 v5

TP-Link TL-MR3420 v5 are simple N300 router with
5-port FE switch and non-detachable antennas.
Its very similar to TP-Link TL-WR841N V13.

Specification:

- MT7628N/N (580 MHz)
- 64 MB of RAM (DDR2)
- 8 MB of FLASH
- 2T2R 2.4 GHz
- 5x 10/100 Mbps Ethernet
- 2x external, non-detachable antennas
- USB 2.0 Port
- UART (J1) header on PCB (115200 8n1)
- 8x LED, 2x button, power input switch

Flash instruction:

The only way to flash LEDE image in mr3420v5 is to use
tftp recovery mode in U-Boot:

1. Configure PC with static IP 192.168.0.225/24 and tftp server.
2. Rename "lede-ramips-mt7628-tplink_tl-mr3420-v5-squashfs-tftp-recovery.bin"
   to "tp_recovery.bin" and place it in tftp server directory.
3. Connect PC with one of LAN ports, press the reset button, power up
   the router and keep button pressed for around 6-7 seconds, until
   device starts downloading the file.
4. Router will download file from server, write it to flash and reboot.

Signed-off-by: Henryk Heisig <hyniu@o2.pl>

target/linux/ramips/base-files/etc/board.d/01_leds

@@ -381,6 +381,12 @@ tl-wr841n-v13)
 	ucidef_set_led_switch "lan4" "lan4" "$boardname:green:lan4" "switch0" "0x10"
 	ucidef_set_led_switch "wan" "wan" "$boardname:green:wan" "switch0" "0x01"
 	;;
+tplink,tl-mr3420-v5)
+	set_usb_led "$boardname:green:usb"
+	set_wifi_led "$boardname:green:wlan"
+	ucidef_set_led_switch "lan" "lan" "$boardname:green:lan" "switch0" "0x1e"
+	ucidef_set_led_switch "wan" "wan" "$boardname:green:wan" "switch0" "0x01"
+	;;
 u25awf-h1)
 	set_wifi_led "u25awf:red:wifi"
 	ucidef_set_led_netdev "eth" "eth" "u25awf:green:lan" "eth0"

target/linux/ramips/base-files/etc/board.d/02_network

@@ -173,6 +173,7 @@ ramips_setup_interfaces()
 	mzk-wdpr|\
 	rb750gr3|\
 	rt-n14u|\
+	tplink,tl-mr3420-v5|\
 	tl-wr840n-v4|\
 	tl-wr840n-v5|\
 	tl-wr841n-v13|\

target/linux/ramips/base-files/etc/diag.sh

@@ -37,6 +37,7 @@ get_status_led() {
 	nbg-419n2|\
 	pwh2004|\
 	r6220|\
+	tplink,tl-mr3420-v5|\
 	tl-wr840n-v4|\
 	tl-wr840n-v5|\
 	tl-wr841n-v13|\