security/vboot: Support enabling EC EFS with EC software sync

If the ChromeOS EC uses EC early firmware selection (EFS), the AP vboot
build must also enable EC EFS. Add an option to control this, passing it
through to vboot.

BUG=b:150742950
TEST=none
BRANCH=none

Signed-off-by: Sam McNally <sammc@chromium.org>
Change-Id: I697e90748e19d15af154011413b30c0f2a0bf52e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39272
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/security/vboot/Kconfig

@@ -260,6 +260,14 @@ config VBOOT_EARLY_EC_SYNC
 	  significantly impact boot time, as this operation will be performed
 	  later in the boot flow if it is disabled here.
 
+config VBOOT_EC_EFS
+	bool "Early firmware selection (EFS) EC"
+	default n
+	help
+	  CrosEC can support EFS: Early Firmware Selection. If it's enabled,
+	  software sync needs to also support it. This setting tells vboot to
+	  perform EFS software sync.
+
 menu "GBB configuration"
 
 config GBB_HWID

src/security/vboot/Makefile.inc

@@ -41,6 +41,7 @@ $$(VBOOT_LIB_$(1)): $(obj)/config.h
 	+FIRMWARE_ARCH=$$(ARCHDIR-$$(ARCH-$(1)-y)) \
 	CC="$$(CC_$(1))" \
 	CFLAGS="$$(VBOOT_CFLAGS_$(1))" VBOOT2="y" \
+	EC_EFS="$(CONFIG_VBOOT_EC_EFS)" \
 	$(MAKE) -C $(VBOOT_SOURCE) \
 		BUILD=$$(abspath $$(dir $$(VBOOT_LIB_$(1)))) \
 		V=$(V) \