x86: samus: Add a target to boot through TPL

Add a version of samus which supports booting from TPL to SPL and then
to U-Boot. This allows TPL to select from an A or B SPL to support
verified boot with field upgrade.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/board/google/Kconfig b/board/google/Kconfig
index d98a5e8..679a0f1 100644
--- a/board/google/Kconfig
+++ b/board/google/Kconfig
@@ -52,6 +52,14 @@
 	  Chrome OS EC connected on LPC, and it provides a 2560x1700 high
 	  resolution touch-enabled LCD display.
 
+config TARGET_CHROMEBOOK_SAMUS_TPL
+	bool "Chromebook samus booting from TPL"
+	help
+	  This is a version of Samus which boots into TPL, then to SPL and
+	  U-Boot proper. This is useful where verified boot must select
+	  between different A/B versions of SPL/U-Boot, to allow upgrading of
+	  almost all U-Boot code in the field.
+
 endchoice
 
 source "board/google/chromebook_link/Kconfig"