ramips: mt7621: Add Arcadyan WE420223-99 support

The Arcadyan WE420223-99 is a WiFi AC simultaneous dual-band access
point distributed as Experia WiFi by KPN in the Netherlands. It features
two ethernet ports and 2 internal antennas.

Specifications
--------------
SOC   : Mediatek MT7621AT
ETH   : Two 1 gigabit ports, built into the SOC
WIFI  : MT7615DN
BUTTON: Reset
BUTTON: WPS
LED   : Power (green+red)
LED   : WiFi (green+blue)
LED   : WPS (green+red)
LED   : Followme (green+red)
Power : 12 VDC, 1A barrel plug

Winbond variant:
RAM   : Winbond W631GG6MB12J, 1GBIT DDR3 SDRAM
Flash : Winbond W25Q256JVFQ, 256Mb SPI
U-Boot: 1.1.3 (Nov 23 2017 - 16:40:17), Ralink 5.0.0.1

Macronix variant:
RAM   : Nanya NT5CC64M16GP-DI, 1GBIT DDR3 SDRAM
Flash : MX25l25635FMI-10G, 256Mb SPI
U-Boot: 1.1.3 (Dec  4 2017 - 11:37:57), Ralink 5.0.0.1

Serial
------
The serial port needs a TTL/RS-232 3V3 level converter! The Serial
setting is 57600-8-N-1. The board has an unpopulated 2.54mm straight pin
header.

The pinout is: VCC (the square), RX, TX, GND.

Installation
------------
See the Wiki page [1] for more details, it comes down to:

1. Open the device, take off the heat sink
2. Connect the SPI flash chip to a flasher, e.g. a Raspberry Pi. Also
   connect the RESET pin for stability (thanks @FPSUsername for reporting)
3. Make a backup in case you want to revert to stock later
4. Flash the squashfs-factory.trx file to offset 0x50000 of the flash
5. Ensure the bootpartition variable is set to 0 in the U-Boot
   environment located at 0x30000

Note that the U-Boot is password protected, this can optionally be
removed. See the forum [2] for more details.

MAC Addresses(stock)
--------------------
+----------+------------------+-------------------+
| use      | address          | example           |
+----------+------------------+-------------------+
| Device   | label            | 00:00:00:11:00:00 |
| Ethernet | + 3              | 00:00:00:11:00:03 |
| 2g       | + 0x020000f00001 | 02:00:00:01:00:01 |
| 5g       | + 1              | 00:00:00:11:00:01 |
+----------+------------------+-------------------+

The label address is stored in ASCII in the board_data partition

Notes
-----
- This device has a dual-boot partition scheme, but OpenWRT will claim
  both partitions for more storage space.

Known issues
------------
- 2g MAC address does not match stock due to missing support for that in
  macaddr_add
- Only the power LED is configured by default

References
----------
[1] https://openwrt.org/inbox/toh/arcadyan/astoria/we420223-99
[2] https://forum.openwrt.org/t/adding-openwrt-support-for-arcadyan-we420223-99-kpn-experia-wifi/132653

Acked-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Signed-off-by: Harm Berntsen <git@harmberntsen.nl>

target/linux/ramips/image/mt7621.mk

@@ -187,6 +187,31 @@ define Device/ampedwireless_ally-00x19k
 endef
 TARGET_DEVICES += ampedwireless_ally-00x19k
 
+define Device/arcadyan_we420223-99
+  $(Device/dsa-migration)
+  $(Device/uimage-lzma-loader)
+  DEVICE_VENDOR := Arcadyan
+  DEVICE_MODEL := WE420223-99
+  DEVICE_ALT0_VENDOR := KPN
+  DEVICE_ALT0_MODEL := Experia WiFi
+  IMAGE_SIZE := 32128k
+  KERNEL_SIZE := 4352k
+  UBINIZE_OPTS := -E 5
+  BLOCKSIZE := 64k
+  PAGESIZE := 1
+  SUBPAGESIZE := 1
+  VID_HDR_OFFSET := 64
+  KERNEL := kernel-bin | append-dtb | lzma | loader-kernel | \
+	uImage none | arcadyan-trx 0x746f435d
+  KERNEL_INITRAMFS := kernel-bin | append-dtb | lzma | loader-kernel | \
+	uImage none
+  IMAGES += factory.trx
+  IMAGE/factory.trx := append-kernel | pad-to $$(KERNEL_SIZE) | append-ubi | check-size
+  IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata
+  DEVICE_PACKAGES := kmod-mt7615-firmware
+endef
+TARGET_DEVICES += arcadyan_we420223-99
+
 define Device/asiarf_ap7621-001
   $(Device/dsa-migration)
   IMAGE_SIZE := 16000k