[ARM] 4767/2: ixp4xx: Add bitops.h include to io.h

Add include of <linux/bitops.h> to io.h to solve compilations errors in
files such as drivers/w1/w1_io.c caused by the ixp4xx version of io.h
using the BIT() macro without including <linux/bitops.h> first.

Signed-off-by: Rod Whitby <rod@whitby.id.au>
Acked-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>