genboardscfg.py: Convert to Python 3

Convert this tool to requiring Python 3.  The bulk of this is done with
the 2to3 tool In addition, we need to use the '//' operator to have our
division result return an int rather than a float and ensure that we use
UTF-8 when reading/writing files.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Tom Rini <trini@konsulko.com>