mainboard/[a-e]: add IS_ENABLED() around Kconfig symbol references

Change-Id: Icca8bac5e67f83dfc5a8f5ef1cb87c6432e0a236
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20342
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/src/mainboard/emulation/qemu-i440fx/northbridge.c b/src/mainboard/emulation/qemu-i440fx/northbridge.c
index d465afe..18dcae3 100644
--- a/src/mainboard/emulation/qemu-i440fx/northbridge.c
+++ b/src/mainboard/emulation/qemu-i440fx/northbridge.c
@@ -167,7 +167,7 @@
 		     IORESOURCE_ASSIGNED;
 }
 
-#if CONFIG_GENERATE_SMBIOS_TABLES
+#if IS_ENABLED(CONFIG_GENERATE_SMBIOS_TABLES)
 static int qemu_get_smbios_data16(int handle, unsigned long *current)
 {
 	struct smbios_type16 *t = (struct smbios_type16 *)*current;
@@ -231,7 +231,7 @@
 	.init			= NULL,
 	.scan_bus		= pci_domain_scan_bus,
 	.ops_pci_bus	= pci_bus_default_ops,
-#if CONFIG_GENERATE_SMBIOS_TABLES
+#if IS_ENABLED(CONFIG_GENERATE_SMBIOS_TABLES)
 	.get_smbios_data	= qemu_get_smbios_data,
 #endif
 };