[MIPS] Remove IT8172-based platforms, ITE 8172G and Globespan IVR support.

As per feature-removal-schedule.txt.

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>