Patch from Lennert Buytenhek

The later ixp2000 models don't need the PCI I/O workaround that we
currently perform.  Add a config option to disable the workaround,
and panic on boot if a kernel without the workaround is booted on a
buggy chip.  As only pre-production ixp2000s need the workaround,
the default is for it not to be configured in.
Signed-off-by: NLennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Deepak Saxena
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>