mb/google/kukui: add flapjack on top of kukui

Add placeholder for future flapjack additions/modifications.

BUG=None
BRANCH=kukui
TEST=build with kukui/flapjack configurations
Signed-off-by: YH Lin <yueherngl@google.com>
Change-Id: Ib9cd39e284f19b9179da73ed9f2b13d97442960e
Reviewed-on: https://review.coreboot.org/c/30859
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/kukui/Kconfig

@@ -1,4 +1,23 @@
-if BOARD_GOOGLE_KUKUI
+##
+## This file is part of the coreboot project.
+##
+## Copyright 2019 Google Inc.
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; version 2 of the License.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+
+# Umbrella option to be selected by variant boards.
+config BOARD_GOOGLE_KUKUI_COMMON
+	def_bool n
+
+if BOARD_GOOGLE_KUKUI_COMMON
 
 config VBOOT
 	select EC_GOOGLE_CHROMEEC_SWITCHES
@@ -25,7 +44,8 @@ config MAINBOARD_DIR
 
 config MAINBOARD_PART_NUMBER
 	string
-	default "Kukui"
+	default "Kukui" if BOARD_GOOGLE_KUKUI
+	default "Flapjack" if BOARD_GOOGLE_FLAPJACK
 
 config DRIVER_TPM_SPI_BUS
 	hex

src/mainboard/google/kukui/Kconfig.name

@@ -1,2 +1,9 @@
+comment "Kukui"
+
 config BOARD_GOOGLE_KUKUI
-	bool "Kukui"
+	bool "->  Kukui"
+	select BOARD_GOOGLE_KUKUI_COMMON
+
+config BOARD_GOOGLE_FLAPJACK
+	bool "->  Flapjack"
+	select BOARD_GOOGLE_KUKUI_COMMON