ARM: legoev3: set serial# env var

This sets the serial# environmet variable instead of using ATAGs on
LEGO MINDSTORMS EV3.

Also fix some nomenclature while we are touching this code (Bluetooth
address is not the same as MAC address, EEPROM version is not the same
as board version).

Signed-off-by: David Lechner <david@lechnology.com>