ramips: add support for TP-Link EC220-G5 v2

ramips: add support for TP-Link EC220-G5 v2

TP-Link EC220-G5 v2 is a dual band router with 4 GbE ports
Advertised as AC1200 for its 867Mbps (2x2) 5GHz band
and 300 Mbps (2x2) 2.4GHz band.

Specs:
- SoC: MediaTek MT7620A
- Ethernet: 4x GbE ports (Realtek RTL8367S)
- Wireless 2.4GHz: MediaTek MT7620A
- Wireless 5GHz: MediaTek MT7612E
- RAM: 64MiB
- ROM: 8MiB (W25Q64BV)
- 2 Buttons (WPS and reset)
- 7 LEDs

Flash instructions via serial console:
1. Rename the factory.bin to to test.bin
2. start a TFTP server from IP address 192.168.0.225 and serve the image named test.bin
3. connect your device to the LAN port
4. power up the router and press 4 on the console to stop the boot process.
5. enter the following commands on the router console
	tftp 0x80060000 test.bin
	erase tplink 0x20000 0x7a0000
	cp.b 0x80060000 0x20000 0x7a0000
	reset

Flash instructions via TFTP:
1. Update orginal firmware of the router to the latest one.
2. Rename openwrt-ramips-mt7620-tplink_ec220-g5-v2-squashfs-tftp-recovery.bin to tp_recovery.bin
3. Change computer IP to 192.168.0.66
4. Run TFTP serwer
5. Start the router with the reset button pressed, the file will be automatically downloaded and after a while the router will restart.
6. After updating, set your computer's IP to DHCP

Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>