The Teensy 3.6 comes with 4096 bytes of EEPROM.
This is commit 1 of 2 to make the EEPROM work.
The next commit changes the core code to wire up the EEPROM.
This moves the config_common.h into the files that include ../config.h,
so that the kint36/config.h does not include it (which would cause
compilation errors).
