Add Makefile for generating EEPROM contents

This generates both a (semi) human-readable text version as well as the
actual binary version.
Add backpack bus firmware

This copies the C code and Makefile from:

https://github.com/Pinoccio/pinoccio-backpack-reference/tree/77ccd4f11e0b1e90f801a557d1fa426c624b5257/firmware
Added schematic PDF directories