Best source of documentation IMHO is from the armbian source. These references should provide the needed description to make a usable device tree. They are mirrored here:
SPI Controller Generic Binding
This binding is for display panels using an Ilitek ILI9341 controller in SPImode.
Device tree bindings for TI's ADS7843, ADS7845, ADS7846, ADS7873, TSC2046SPI driven touch screen controllers.
The other tidbit of info is the structure of a gpio cell property. AFAIK the numeric values for <&pio 0 2 1> refers to pin group 0 = A, pin offset 2 (A2), and pull-up flag.
Also, it is required to configure and activate the device trees. Configuration, like param_spidev_spi_bus=0, is still a mystery to me. armbian-config doesn't automatically add these items to /boot/armbianEnv.txt so this can be a major source of frustration.
My example /boot/armbianEnv.txt:
verbosity=7
dtdebug=7
bootlogo=false
console=serial
disp_mode=1920x1080p60
overlay_prefix=sun50i-h5
overlays=spi-spidev
param_spidev_spi_bus=0
user_overlays=sun50i-h5-ili9341
usbstoragequirks=0x2537:0x1066:u,0x2537:0x1068:u
rootdev=UUID=8d9edae5-2ab9-4c42-933e-ee4235da815f
rootfstype=ext4
I created sun50i-h5-ili9341 using the referenced documentation as a guide.