ramips: add support for I-O DATA WN-AX1167GR

ramips: add support for I-O DATA WN-AX1167GR

I-O DATA WN-AX1167GR is a 2.4/5 GHz band 11ac router, based on
MediaTek MT7621A.

Specification:

- MT7621A (2-Cores, 4-Threads)
- 64 MB of RAM (DDR2)
- 16 MB of Flash (SPI)
- 2T2R 2.4/5 GHz
- 5x 10/100/1000 Mbps Ethernet
- 2x LEDs, 4x keys (2x buttons, 1x slide switch)
- UART header on PCB
  - Vcc, GND, TX, RX from ethernet port side
  - baudrate: 115200 bps (U-Boot, OpenWrt)

Stock firmware:

In the stock firmware, WN-AX1167GR has two os images each composed of
Linux kernel and rootfs.
These images are stored in "Kernel" and "app" partition of the
following partitions, respectively.

(excerpt from dmesg):

MX25L12805D(c2 2018c220) (16384 Kbytes)
mtd .name = raspi, .size = 0x01000000 (16M) .erasesize = 0x00010000 (64K) .numeraseregions = 0
Creating 10 MTD partitions on "raspi":
0x000000000000-0x000001000000 : "ALL"
0x000000000000-0x000000030000 : "Bootloader"
0x000000030000-0x000000040000 : "Config "
0x000000040000-0x000000050000 : "Factory"
0x000000050000-0x000000060000 : "iNIC_rf"
0x000000060000-0x0000007e0000 : "Kernel"
0x000000800000-0x000000f80000 : "app"
0x000000f90000-0x000000fa0000 : "Key"
0x000000fa0000-0x000000fb0000 : "backup"
0x000000fb0000-0x000001000000 : "storage"

The flag for boot partition is stored in "Key" partition, and U-Boot
reads this and determines the partition to boot.

If the image that U-Boot first reads according to the flag is
"Bad Magic Number", U-Boot then tries to boot from the other image.
If the second image is correct, change the flag to the number
corresponding to that image and boot from that image.

(example):

## Booting image at bc800000 ...
Bad Magic Number,FFFFFFFF
Boot from KERNEL 1  !!
## Booting image at bc060000 ...
   Image Name:   MIPS OpenWrt Linux-4.14.50
   Image Type:   MIPS Linux kernel Image (lzma compressed)
   Data Size:    1865917 Bytes = 1.8 MB
   Load Address: 80001000
   Entry Point:  80001000
   Verifying Checksum ... OK
   Uncompressing Kernel Image ... OK
raspi_erase_write: offs:f90000, count:34
.
.
Done!

Starting kernel ...

Flash instruction using factory image:

1. Connect the computer to the LAN port of WN-AX1167GR
2. Connect power cable to WN-AX1167GR and turn on it
3. Access to "192.168.0.1" on the web browser and open firmware
update page ("ファームウェア")
4. Select the OpenWrt factory image and perform firmware update
5. On the initramfs image, execute "mtd erase firmware" to erase stock
firmware and execute sysupgrade with sysupgrade image for WN-AX1167GR
6. Wait ~180 seconds to complete flasing

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>