Adding address offset to all MBoard and DBoard EEPROM reads. This
matches what we're doing for the user portion of the EEPROM, and
allows us to share access to an EEPROM.
Zlib's crc32 outputs signed values in python2 and unsigned values in
python3. As per this page (https://docs.python.org/2/library/zlib.html)
0xffffffff can be AND'd to the result to get the same value between
Python versions
