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/i82801ix/lpc.c

@@ -369,7 +369,7 @@ static void enable_clock_gating(void)
 	RCBA32(0x38c0) |= 7;
 }
 
-#if CONFIG_HAVE_SMI_HANDLER
+#if IS_ENABLED(CONFIG_HAVE_SMI_HANDLER)
 static void i82801ix_lock_smm(struct device *dev)
 {
 #if TEST_SMM_FLASH_LOCKDOWN
@@ -464,7 +464,7 @@ static void lpc_init(struct device *dev)
 	/* Interrupt 9 should be level triggered (SCI) */
 	i8259_configure_irq_trigger(9, 1);
 
-#if CONFIG_HAVE_SMI_HANDLER
+#if IS_ENABLED(CONFIG_HAVE_SMI_HANDLER)
 	i82801ix_lock_smm(dev);
 #endif
 }