soc/amd/picasso: introduce and use chipset device tree

The chipset devicetree only has the essential PCIe devices enabled that
are needed for the SoC code to work. It also defines aliases for all
PCIe devices that can be used to reference the devices in the mainboard-
specific devicetrees and devicetree overrides. To make the change easier
to review that part will be done in a follow-up patch.

Despite missing in the PPR, device pci 18.7 exists on Picasso.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I6b7c3fd32579a23539594672593a243172c161c7
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50626
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/soc/amd/picasso/Kconfig

@@ -71,6 +71,10 @@ config CPU_SPECIFIC_OPTIONS
 config SOC_AMD_COMMON_BLOCK_UCODE_SIZE
 	default 3200
 
+config CHIPSET_DEVICETREE
+	string
+	default "soc/amd/picasso/chipset.cb"
+
 config FSP_M_FILE
 	string "FSP-M (memory init) binary path and filename"
 	depends on ADD_FSP_BINARIES