ath79: add support for NEC Aterm WG1200CR

ath79: add support for NEC Aterm WG1200CR

NEC Aterm WG1200CR is a 2.4/5 GHz band 11ac router,
based on Qualcomm Atheros QCA9563.

Specification:

- SoC		: Qualcomm Atheros QCA9563
- RAM		: DDR2 128 MiB
- Flash		: SPI-NOR 8 MiB
- WLAN		: 2.4/5 GHz 2T2R
  - 2.4 GHz	: QCA9563 (SoC)
  - 5 GHz	: QCA9888
- Ethernet	: 2x 10/100/1000 Mbps
  - Switch	: QCA8334
- LEDs/Input	: 12x/4x (2x buttons, 1x slide-switch)
- UART		: through-hole on PCB
  - JP1: Vcc, GND, NC, TX, RX from power connector side
  - 115200 bps

Flash instruction using factory image:

1. Boot WG1200CR normaly
2. Access to "http://192.168.10.1/" and open firmware update page
("ファームウェア更新")
3. Select the OpenWrt factory image and click update ("更新") button
to perform firmware update
4. Wait ~150 seconds to complete flashing

Known issues:

- cannot be controlled LEDs other than Power (Green/Red)
  - only Power LEDs are connected to SoC GPIO; other LEDs
    connected to the gpiochip on ath10k chip (QCA9888)

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com> [commit
message formatting]