southbridge/intel: add IS_ENABLED() around Kconfig symbol references

Change-Id: I2b532522938123bb7844cef94cda0b44bcb98e45
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20350
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/southbridge/intel/lynxpoint/pmutil.c

@@ -26,7 +26,7 @@
 #include <console/console.h>
 #include "pch.h"
 
-#if CONFIG_INTEL_LYNXPOINT_LP
+#if IS_ENABLED(CONFIG_INTEL_LYNXPOINT_LP)
 #include "lp_gpio.h"
 #endif