spigen overlays to be placed into 'base'. one for RPI-B, the other for RPI-2.
requires loader.conf 'fdt_overlays' entry for the correct overlay (either spigen-rpi-b.dtbo or spigen-rpi2.dtbo)
Implements 3 spigen devices on RPI2, but only 2 on RPi-B. This is because RPi-B uses GPIO16 for an LED, and it therefore cannot be used for SPI.
Needs DS15301 if you want a relationship between the cs pin and the spigen device name.