src/include: add IS_ENABLED() around Kconfig symbol references

Change-Id: I2fbe6376a1cf98d328464556917638a5679641d2
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20354
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/include/device/pci.h

@@ -15,7 +15,7 @@
 #ifndef PCI_H
 #define PCI_H
 
-#if CONFIG_PCI
+#if IS_ENABLED(CONFIG_PCI)
 
 #include <stdint.h>
 #include <stddef.h>