Can you tell me how you got the point of having /dev/spidevX.Y? With a ]ARMBIAN 5.37 user-built Debian GNU/Linux 9[ I see things on /boot/dtb/overlay/README.* that suggests that I ought to be able the NOR by adding:
spi-jedec-nor to overlays in armbianEnv.txt, and I see uboot loading that dtbo file at boot. There is a chip on the bottom of the board (which is from spring 2017).
https://linux-sunxi.org/Xunlong_Orange_Pi_Zero says that I need to insert some DTB and gives it, but I was sure that it was already available in the overlays. I got something to give me a spi0.1 in dmesg, but no /dev or mtd entries.
https://linux-sunxi.org/Bootable_SPI_flash gives far more details about the state, but not details as to how to do the DTB work.
I'm pretty sure that Armbian has the right drivers built-in, but I'm really unclear how to enable them. (Even as a kernel guy, DTB is still a bit of black magic to me)