Force SB700 bootblock code to use I/O for PCI config cycles.

Force SB700 bootblock code to use I/O for PCI config cycles.

If PCI config cycles use MMIO instead of I/O in the SB700
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 specified
by the mainboards Kconfig.

Change-Id: I15a89a27645edf594d14ef20f129f75a315e9672
Signed-off-by: Marc Jones <marcj303@gmail.com>
Reviewed-on: http://review.coreboot.org/631
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>