mainboard/google/reef: support verstage

The chromeos.c suport needs to be linked into verstage so it will
link.

Change-Id: If85e232a3721443edfbbd278b32f72302f13f3a8
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/14973
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/reef/Makefile.inc

@@ -6,3 +6,5 @@ romstage-$(CONFIG_CHROMEOS) += chromeos.c
 ramstage-$(CONFIG_CHROMEOS) += chromeos.c
 ramstage-y += ec.c
 ramstage-y += mainboard.c
+
+verstage-$(CONFIG_CHROMEOS) += chromeos.c