soc/amd/cezzane: Add a minimal chipset tree

This change adds a minimal chipset tree with only two devices:
1. Domain
2. GNB root complex

This allows sconfig to generate the config structure for SoC root
device that is used by config_of_soc().

Change-Id: I7e08ecf4b9556dc9325bd5a6a51566a949ceb73f
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49245
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Jason Glenesk <jason.glenesk@gmail.com>

src/soc/amd/cezanne/Kconfig

@@ -26,6 +26,10 @@ config SOC_SPECIFIC_OPTIONS
 	select SOC_AMD_COMMON_BLOCK_SMI
 	select SOC_AMD_COMMON_BLOCK_TSC_FAM17H_19H
 
+config CHIPSET_DEVICETREE
+	string
+	default "soc/amd/cezanne/chipset.cb"
+
 config EARLY_RESERVED_DRAM_BASE
 	hex
 	default 0x2000000

src/soc/amd/cezanne/chipset.cb

@@ -0,0 +1,5 @@
+chip soc/amd/cezanne
+	device domain 0 on
+		device pci 00.0 alias gnb on end
+	end
+end