google/parrot: make chromeos.c compilation conditional on CONFIG_CHROMEOS

No reason to compile/include chromeos.c for non-ChromeOS builds

Change-Id: Ie8ef1f4c521b2a7308941299f2501073937bdf4a
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/19959
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/google/parrot/Makefile.inc

@@ -15,6 +15,6 @@
 
 ramstage-y += ec.c
 
-romstage-y += chromeos.c
-ramstage-y += chromeos.c
+romstage-$(CONFIG_CHROMEOS) += chromeos.c
+ramstage-$(CONFIG_CHROMEOS) += chromeos.c
 romstage-y += gpio.c