filogic: add support for ASUS TUF-AX4200

Hardware
--------
SOC:   MediaTek MT7986
RAM:   512MB DDR3
FLASH: 256MB SPI-NAND (Winbond W25N02KV)
WIFI:  Mediatek MT7986 DBDC 802.11ax 2.4/5 GHz
ETH:   MediaTek MT7531 Switch
       MaxLinear GPY211C 2.5 N-Base-T PHY
UART:  3V3 115200 8N1 (Pinout silkscreened / Do not ocnnect VCC)

Installation
------------

1. Download the OpenWrt initramfs image. Copy the image to a TFTP server
   reachable at 192.168.1.66/24. Rename the image to tufax4200.bin.

2. Connect the TFTP server to the AX4200. Conect to the serial console,
   interrupt the autoboot process by pressing '4' when prompted.

3. Download & Boot the OpenWrt initramfs image.

   $ setenv ipaddr 192.168.1.1
   $ setenv serverip 192.168.1.66
   $ tftpboot 0x46000000 tufax4200.bin
   $ bootm 0x46000000

4. Wait for OpenWrt to boot. Transfer the sysupgrade image to the device
   using scp and install using sysupgrade.

   $ sysupgrade -n <path-to-sysupgrade.bin>

Missing features
----------------

 - The LAN port LEDs are driven by the switch but OpenWrt does not
   correctly configure the output.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/mediatek/image/filogic.mk

@@ -38,6 +38,24 @@ define Build/mt7986-gpt
 	rm $@.tmp
 endef
 
+define Device/asus_tuf-ax4200
+  DEVICE_VENDOR := ASUS
+  DEVICE_MODEL := TUF-AX4200
+  DEVICE_DTS := mt7986a-asus-tuf-ax4200
+  DEVICE_DTS_DIR := ../dts
+  DEVICE_DTS_LOADADDR := 0x47000000
+  DEVICE_PACKAGES := kmod-usb3
+  IMAGES := sysupgrade.bin
+  KERNEL_LOADADDR := 0x48000000
+  KERNEL = kernel-bin | lzma | \
+	fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb
+  KERNEL_INITRAMFS := kernel-bin | lzma | \
+	fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb with-initrd | pad-to 64k
+  IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata
+endef
+TARGET_DEVICES += asus_tuf-ax4200
+
+
 define Device/bananapi_bpi-r3
   DEVICE_VENDOR := Bananapi
   DEVICE_MODEL := BPi-R3