ath79: add support for TP-Link RE455 v1

ath79: add support for TP-Link RE455 v1

TP-Link RE455 v1 is a dual band router/range-extender based on
Qualcomm/Atheros QCA9563 + QCA9880.

This device is nearly identical to RE450 v3

Specification:

- 775 MHz CPU
- 64 MB of RAM (DDR2)
- 8 MB of FLASH (SPI NOR)
- 3T3R 2.4 GHz
- 3T3R 5 GHz
- 1x 10/100/1000 Mbps Ethernet (AR8033 PHY)
- 7x LED, 4x button
- UART header on PCB[1]

Flash instruction:
Apply factory image in OEM firmware web-gui.

[1] Didn't work, probably need to short unpopulated resistor R64
    and R69 as RE450v3

Signed-off-by: Roberto Valentini <valantin89@gmail.com>