mainboard/[g-l]: add IS_ENABLED() around Kconfig symbol references

Change-Id: I1f906c8c465108017bc4d08534653233078ef32d
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20343
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/mainboard/google/slippy/acpi_tables.c

@@ -55,7 +55,7 @@ void acpi_create_gnvs(global_nvs_t *gnvs)
 	gnvs->tpmp = 1;
 
 
-#if CONFIG_CHROMEOS
+#if IS_ENABLED(CONFIG_CHROMEOS)
 	gnvs->chromeos.vbt2 = google_ec_running_ro() ?
 		ACTIVE_ECFW_RO : ACTIVE_ECFW_RW;
 #endif