iop: Make IOP ATU window debug readable

Make the inbound and outbound memory windows debugging meaningful to
those who don't know what the register names for the ATU mean.  IOW,
use plain english rather than register jargon.

Cc: Lennert Buytenhek <kernel@wantstofly.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>