x86: Fix up CONFIG_X86_64 check

When SPL and U-Boot proper have different settings for this flag, we need to
use the correct one. Fix this up in the interrupt code.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/cpu/i386/interrupt.c

@@ -234,7 +234,7 @@ int disable_interrupts(void)
 {
 	long flags;
 
-#ifdef CONFIG_X86_64
+#if CONFIG_IS_ENABLED(X86_64)
 	asm volatile ("pushfq ; popq %0 ; cli\n" : "=g" (flags) : );
 #else
 	asm volatile ("pushfl ; popl %0 ; cli\n" : "=g" (flags) : );