soc/amd/common: Drop ACPIMMIO bank for SMBus device PCI config

soc/amd/common: Drop ACPIMMIO bank for SMBus device PCI config

The PCI config space of the SMBus device has a secondary mapping as an
ACPIMMIO bank. Since the PCI device is on bus 0, it's already available
early in boot after the enable_pci_mmconf call, so there's no need to
use the ACPIMMIO mapping instead of the PCI config space mapping.
Verstage on PSP could theoretically access the PCI config space via the
0xcf8/0xcfc register pair, but since verstage on PSP doesn't have the
ACPIMMIO mapping anyway, we won't loose any functionality here.

Change-Id: I5c8ce8de0a6ab0ed41e7e8a5980d0f0510aaa993
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42685
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>