soc/amd/common/data_fabric/domain: write _BBN method in SSDT

Instead of having PCI0's _BBN method in the DSDT that always returns 0,
use acpigen_write_BBN to generate the _BBN method that returns the first
PCI bus number in the PCI domain/host bridge.

TEST=On mandolin the _BBN method in the _SB/PCI0 scope is now in the
SSDT instead of the DSDT, but still returns 0.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I8badeb0064b498d3f18217ea24bff73676913b02
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74992
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/common/block/data_fabric/domain.c

@@ -243,6 +243,9 @@ void amd_pci_domain_fill_ssdt(const struct device *domain)
 	}
 
 	acpigen_write_resourcetemplate_footer();
+
+	acpigen_write_BBN(domain->link_list->secondary);
+
 	/* Scope */
 	acpigen_pop_len();
 }

src/soc/amd/picasso/acpi/northbridge.asl

@@ -6,11 +6,6 @@ Name(_CID, EISAID("PNP0A03"))	/* PCI Root Bridge */
 
 /* Describe the Northbridge devices */
 
-Method(_BBN, 0, NotSerialized)	/* Bus number = 0 */
-{
-	Return(0)
-}
-
 Method(_STA, 0, NotSerialized)
 {
 	Return(0x0f)	/* Status is visible */