ath79: add support for NEC Aterm WG2200HP

ath79: add support for NEC Aterm WG2200HP

NEC Aterm WG2200HP is a 2.4/5 GHz band 11ac (Wi-Fi 5) router, based on
QCA9558.

Specification:

- SoC              : Qualcomm Atheros QCA9558
- RAM              : DDR2 128 MiB (2x ESMT M14D5121632A)
- Flash            : SPI-NOR 16 MiB (Macronix MX25L12835FM2I-10G)
- WLAN             : 2.4/5 GHz
  - 2.4 GHz        : 3T3R (Qualcomm Atheros QCA9558 (SoC))
  - 5 GHz          : 4T4R (Qualcomm Atheros QCA9984)
- Ethernet         : 5x 10/100/1000 Mbps
  - switch         : Qualcomm Atheros QCA8337
- LEDs/Keys (GPIO) : 12x/4x
- UART             : through-hole on PCB
  - assignment     : 3.3V, GND, NC, TX, RX from tri-angle marking
  - settings       : 9600n8
- USB              : 1x USB 2.0 Type-A
- Power            : 12 VDC, 1.5 A (Max: 20 W)
- Stock OS         : NetBSD based

Flash instruction using initramfs-factory.bin image:

 1. Connect and open serial console
 2. Power on WG2200HP and interrupt bootloader by ESC key
 3. Login to the bootloader CLI with a password "chiron"
 4. Start TFTP server by "tftpd" command
 5. Upload initramfs-factory.bin via tftp from your computer

    example (Windows): tftp -i 192.168.0.1 PUT initramfs-factory.bin

 6. Boot initramfs image by "boot" command
 7. On the initramfs image, back up the stock bootloader and firmware if
    needed
 8. Upload (or download) uboot.bin and sysupgrade.bin image to the device
 9. Rplace the bootloader with a uboot.bin image

    mtd write <uboot.bin image> bootloader

10. Perform sysupgrade with a sysupgrade.bin image
11. Wait ~120 seconds to complete flashing

Notes:

- All LEDs are connected to the Diodes PI4IOE5V9539LE I2C Expander chip.
  (compatible with NXP PCA9539)

- The stock bootloader requires an unknown filesystem on firmware area
  in the flash. Booting of OpenWrt from that filesystem cannot be
  handled, so the bootloader needs to be replaced to mainline U-Boot
  before OpenWrt installation.

- The data length of blocks in firmware image will be checked
  (4M < threshold < 6M) on the stock WebUI of all versions, and
  initramfs-factory.bin image of OpenWrt has the larger block data for
  initramfs image. So that image cannot be applied to the stock WebUI
  at all.

MAC addresses:

LAN    : 98:F1:99:xx:xx:7C (config, 0x6  (hex))
WAN    : 98:F1:99:xx:xx:7D (config, 0xc  (hex))
2.4 GHz: 98:F1:99:xx:xx:7E (config, 0x0  (hex))
5 GHz  : 98:F1:99:xx:xx:7F (config, 0x12 (hex))

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17584
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>