serial: add support for ITE 887x chips

Add support for the it887x-chips (PCI) manufactured by ITE.

Signed-off-by: Niels de Vos <niels.devos@wincor-nixdorf.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>