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

Some of these can be changed from #if to if(), but that will happen
in a follow-on commmit.

Change-Id: Id5bc8b75b1fa372f31982b8636f1efa4975b61a5
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20346
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/src/northbridge/intel/sandybridge/northbridge.c b/src/northbridge/intel/sandybridge/northbridge.c
index 635e321..3c0b9ec 100644
--- a/src/northbridge/intel/sandybridge/northbridge.c
+++ b/src/northbridge/intel/sandybridge/northbridge.c
@@ -100,7 +100,7 @@
 	reserved_ram_resource(dev, index++, 0xc0000 >> 10,
 			(0x100000 - 0xc0000) >> 10);
 
-#if CONFIG_CHROMEOS_RAMOOPS
+#if IS_ENABLED(CONFIG_CHROMEOS_RAMOOPS)
 	reserved_ram_resource(dev, index++,
 			CONFIG_CHROMEOS_RAMOOPS_RAM_START >> 10,
 			CONFIG_CHROMEOS_RAMOOPS_RAM_SIZE >> 10);