nb/amd: 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: I763cbbc31dcd4cdd128c04793a742ab6daaf5f0c
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20345
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/northbridge/amd/pi/00730F01/northbridge.c b/src/northbridge/amd/pi/00730F01/northbridge.c
index 960078e..de2059d 100644
--- a/src/northbridge/amd/pi/00730F01/northbridge.c
+++ b/src/northbridge/amd/pi/00730F01/northbridge.c
@@ -391,7 +391,7 @@
 	 * we only deal with the 'first' vga card */
 	for (link = dev->link_list; link; link = link->next) {
 		if (link->bridge_ctrl & PCI_BRIDGE_CTL_VGA) {
-#if CONFIG_MULTIPLE_VGA_ADAPTERS
+#if IS_ENABLED(CONFIG_MULTIPLE_VGA_ADAPTERS)
 			extern device_t vga_pri; // the primary vga device, defined in device.c
 			printk(BIOS_DEBUG, "VGA: vga_pri bus num = %d bus range [%d,%d]\n", vga_pri->bus->secondary,
 					link->secondary,link->subordinate);