soc/intel/xeon_sp/spr: Enable 512 MMCONF buses by default

soc/intel/xeon_sp/spr: Enable 512 MMCONF buses by default

As of now coreboot only supported one PCI segment group and thus the
MMCONF size had to be limited to 256 buses on ibm/sbp1. Since the
default FSP doesn't allow to disable unused IIO stacks a patched
version had to be used. Those unused IIO stacks consume lots of PCI
bus ranges, leaving no free buses for the secondary side behind PCI
bridges. The IIO disable mechanism doesn't work after ACPI G3 exit
and thus requires multiple reboots when the previous state was G3.

Since coreboot now supports multi PCI segment groups enable 512
MMCONF buses on 4S platforms by default and drop the IIO stack
disable UPDs on ibm/sbp1. This allows to boot faster without the
need for a patched FSP.

The use of multiple PCI segment groups might prevent legacy software
from working properly, however the only board where multiple PCI
segment groups are used uses u-root as default payload.

TEST=Booted on ibm/sbp1 to ubuntu22.04 using two PCI segment groups.
TEST=intel/archercity CRB

Change-Id: I4e6e5eca1196d4ab50e43b4b58d24eca444ab519
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/81187
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>