Replace existing gte_divider with MAME's version

The original code did not have a license header, and as a result was
licensed under the GPLv2 which means that it was impossible to link it
with LGPL code.

The new code originates from MAME and is under a BSD-3-Clause license,
which is GPL-compatible, and also much cleaner.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>