mb/google/guybrush: Build chromeos.c in verstage

Before attempting another commit 6260bf71 (vboot_logic: Set
VB2_CONTEXT_EC_TRUSTED in verstage_main), ensure that guybrush builds
chromeos.c in verstage to call get_ec_is_trusted() in vboot
verstage_main().

Signed-off-by: Hsuan Ting Chen <roccochen@chromium.org>
Change-Id: Ic22519fdde1b18f6ce0237022dee02ca37181a74
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58193
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/mainboard/google/guybrush/Makefile.inc

@@ -18,6 +18,7 @@ ramstage-y += ec.c
 ramstage-$(CONFIG_CHROMEOS) += chromeos.c
 
 verstage-y += verstage.c
+verstage-$(CONFIG_CHROMEOS) += chromeos.c
 
 subdirs-y += variants/baseboard
 subdirs-y += variants/$(VARIANT_DIR)