Well its equivalent so other than vendor not beeing in a database does not count as custom in my books, but that is beside the point. Armbian correctly recognizes the size and I can write to it and that is important.
Now flashing an existing image is simple. My preferred way is dd as described by Piter75:
dd if=uboot.img of=/dev/mtdblock0 bs=4K for u-boot images
and
dd if=idbloader.img of=/dev/mtdblock0 seek=64 bs=512 conv=sync
dd if=u-boot.itb of=/dev/mtdblock0 seek=16384 bs=512 conv=sync
if used with image tree blob. Nice thing is that if new u-boot hangs or does not boot I can just short pin 23-25 to boot from SD card and try again. Since I have an 8Mb flash I would really like to bake in m.2 to SATA drivers - for ASM1166 in my case. Any pointers are welcome.
DeMo