mediatek: add factory image for ipTIME AX3000SM

Adds the capability to flash the factory image using the OEM recovery
software, ipTIME Firmware Wizard(11ac).

Installation
------------
1. Download the OEM recovery software from the manufacturer's website
2. Download the *squashfs-factory.bin file from the OpenWrt website
3. Press a reset button, and power up the router(keep pressing the reset button)
4. Wait more than 10 seconds until the CPU LED stop blinking
5. Connect the router(LAN port) to the PC
6. Run the OEM recovery software and follow the instructions
7. Select the *squashfs-factory.bin file during the router recovery process
8. Wait for the router to boot from *squashfs-factory.bin

Signed-off-by: Donghyun Ko <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/19497
(cherry picked from commit 0e4a69e340083f78ef1e6ec148042d8cde415b78)
Signed-off-by: Donghyun Ko <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/19928
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/mediatek/image/filogic.mk

@@ -1055,8 +1055,16 @@ define Device/iptime_ax3000sm
   DEVICE_MODEL := AX3000SM
   DEVICE_DTS := mt7981b-iptime-ax3000sm
   DEVICE_DTS_DIR := ../dts
-  DEVICE_PACKAGES := kmod-mt7915e kmod-mt7981-firmware mt7981-wo-firmware
+  BLOCKSIZE := 128k
+  PAGESIZE := 2048
+  IMAGE_SIZE := 32768k
+  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
+  IMAGES := factory.bin sysupgrade.bin
+  IMAGE/factory.bin := sysupgrade-tar | append-metadata | check-size | iptime-crc32 ax3ksm
   IMAGE/sysupgrade.bin := sysupgrade-tar | append-metadata
+  DEVICE_PACKAGES := kmod-mt7915e kmod-mt7981-firmware mt7981-wo-firmware
   SUPPORTED_DEVICES += mediatek,mt7981-spim-snand-rfb
 endef
 TARGET_DEVICES += iptime_ax3000sm