mb/google/mancomb: Enable mancomb variant

BUG=b:182211161
TEST=builds

Signed-off-by: Eric Lai <ericr_lai@compal.corp-partner.google.com>
Change-Id: I554e7193494a4bbf005aaf2fb4efd6ded383fe07
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51369
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Mathew King <mathewk@chromium.org>

src/mainboard/google/mancomb/Kconfig

@@ -39,10 +39,18 @@ config AMD_FWM_POSITION_INDEX
 	help
 	  TODO: might need to be adapted for better placement of files in cbfs
 
+config VARIANT_DIR
+	string
+	default "mancomb" if BOARD_GOOGLE_MANCOMB
+
 config DEVICETREE
 	string
 	default "variants/baseboard/devicetree.cb"
 
+config OVERRIDE_DEVICETREE
+	string
+	default "variants/\$(CONFIG_VARIANT_DIR)/overridetree.cb"
+
 config MAINBOARD_FAMILY
 	string
 	default "Google_Mancomb"

src/mainboard/google/mancomb/Makefile.inc

@@ -6,4 +6,7 @@ ramstage-y += mainboard.c
 ramstage-$(CONFIG_CHROMEOS) += chromeos.c
 
 subdirs-y += variants/baseboard
+subdirs-y += variants/$(VARIANT_DIR)
+
 CPPFLAGS_common += -I$(src)/mainboard/$(MAINBOARDDIR)/variants/baseboard/include
+CPPFLAGS_common += -I$(src)/mainboard/$(MAINBOARDDIR)/variants/$(VARIANT_DIR)/include

src/mainboard/google/mancomb/variants/mancomb/overridetree.cb

@@ -0,0 +1,4 @@
+chip soc/amd/cezanne
+	device domain 0 on
+	end # domain
+end # chip soc/amd/cezanne