kconfiglib: Update to the 12.14.0 release

A large number of changes have happened upstream since our last sync
which was to 375506d.  The reason to do the upgrade at this point is for
improved Python 3 support.

As part of this upgrade we need to update moveconfig.py and
genboardscfg.py the current API.  This is:
- Change "kconfiglib.Config" calls to "kconfiglib.Kconfig"
- Change get_symbol() calls to syms.get().
- Change get_value() to str_value.

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