[ARM] 3302/1: make pci=firmware the default for ixp2000

Patch from Lennert Buytenhek

Most ixp2000 boards don't actually work if pci=firmware isn't used, so
the defconfig isn't really the right place to specify this.  Instead of
specifying it in the defconfigs, make the relevant board code take care
of setting pci=firmware.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Deepak Saxena <dsaxena@plexity.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>