google/cosmos: romstage needs the accessor functions for buttons

In Chrome OS mode, the romstage tries to interpret the various buttons on the
device, so it needs access to the accessor functions.

Change-Id: Iecfd37e79883d826e15c474d77095fbbbb2b7cea
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/10705
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/google/cosmos/Makefile.inc

@@ -26,6 +26,7 @@ verstage-y += chromeos.c
 verstage-y += reset.c
 
 romstage-y += boardid.c
+romstage-y += chromeos.c
 romstage-y += romstage.c
 romstage-y += reset.c