ath79: add support for TP-Link RE350K v1

ath79: add support for TP-Link RE350K v1

TP-Link RE350K v1 (FCC ID: TE7RE350K) is a wall-plug AC1200 Wi-Fi range
extender with 'Kasa Smart' support. Device is based on Qualcomm/Atheros
QCA9558 + QCA9882 + AR8035 platform and is available only on US market.

Specification:

- 720/600/200 MHz (CPU/DDR/AHB)
- 128 MB of RAM (DDR2)
- 16 MB of flash (SPI NOR)
- 1x 1 Gbps Ethernet (AR8035)
- 2T2R 2.4 GHz (QCA9558), with ext. PA (SE2565T) and LNA (SKY65971-11)
- 2T2R 5 GHz (QCA9882), with ext. PA (SE5003L1-R) and LNA (SKY65981-11)
- 2x U.FL connector on PCB
- 2x dual-band PCB antennas
- 1x LED, 2x dual-color LED (all driven by GPIO)
- 3x button (app config, led, reset)
- 1x mechanical on/off slide switch
- 1x UART (4-pin, 2.54 mm pitch) header on PCB
- 1x JTAG (8-pin, 1.27 mm pitch) header on PCB

Flash instruction:
Use 'factory' image directly in vendor GUI (default IP: 192.168.0.254,
default credentials: admin/admin).

Warning:
This device does not include any kind of recovery mechanism in U-Boot.

Vendor firmware access:
You can access vendor firmware over serial (RX line requires jumper
resistor in R306 place, near XTAL) with: root/sohoadmin credentials.

Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>