ramips: add factory image for ipTIME AX2004M

ramips: add factory image for ipTIME AX2004M

Unlike the recovery image, this initramfs-factory image can be flashed
using the stock firmware web interface (from any active boot partition),
as well as the bootloader recovery web page. Drop the recovery image in
favor of the factory image.

Installation via stock/recovery web interface:
1.  Flash **initramfs-factory** image through the web page.
2.  Boot into OpenWrt and perform sysupgrade with sysupgrade image.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>