Force SB600 bootblock to use I/O for PCI config

Force SB600 bootblock to use I/O for PCI config

If PCI config cycles use MMIO instead of I/O in the SB600 bootblock
code the cycles will go nowhere since the MMIO feature hasn't been
configured yet. This change forces the cycles to use I/O and
configures the southbridge decode range to what is defined by the
mainboards Kconfig.

Change-Id: I85297237f32f37b3fc1ff5b488cca0a43bcf20fd
Signed-off-by: Marc Jones <marcj303@gmail.com>
Reviewed-on: http://review.coreboot.org/632
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>