soc/amd/common/include/ioapic: make IOAPIC IDs not depend on MAX_CPUS

Since the APIC bus isn't used since a long time and the IOAPIC and LAPIC
talk to each other via the system bus, there is no longer the
requirement that the IOAPIC IDs mustn't overlap with the LAPIC IDs that
start at 0 and end at CONFIG_MAX_CPUS - 1. The current Intel code uses 2
as the IOAPIC ID while most of their CPUs have more than 2 logical cores
resulting in the IOAPIC having the same ID as one of the LAPICs.

All chipsets in soc/amd use the defines for FCH_IOAPIC_ID and
GNB_IOAPIC_ID for initializing the IOAPIC register, writing both MADT
and IVRS ACPI tables and there's no MPTable support for those SoCs that
might also rely on those IDs being consistent.

This patch changes the definitions for FCH_IOAPIC_ID and GNB_IOAPIC_ID
from CONFIG_MAX_CPUS and CONFIG_MAX_CPUS + 1 to 0 and 1. This also makes
sure that the IOAPIC IDs still fit in 4 bits despite Cezanne having a
CONFIG_MAX_CPUS of 16 resulting in the IOAPIC IDs being larger than 4
bits with the old code. While the Cezanne FCH IOAPIC supports 8 bits of
IOAPIC IDs, this is non-standard.

TEST=AMD Mandolin and Google Liara still work.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Suggested-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Change-Id: Id3a356480bb8407e0347cb5cef691fde7edc8deb
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55430
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/soc/amd/common/block/include/amdblocks/ioapic.h

@@ -3,7 +3,8 @@
 #ifndef AMD_BLOCK_IOAPIC_H
 #define AMD_BLOCK_IOAPIC_H
 
-#define FCH_IOAPIC_ID		CONFIG_MAX_CPUS
+/* Since the old APIC bus isn't used any more, the IOAPIC IDs can be < CONFIG_MAX_CPUS */
-#define GNB_IOAPIC_ID		(CONFIG_MAX_CPUS + 1)
+#define FCH_IOAPIC_ID		0
+#define GNB_IOAPIC_ID		1
 
 #endif /* AMD_BLOCK_IOAPIC_H */