rtc: Use CONFIG_X86 instead of __I386__

For 64-bit x86, __I386__ should perhaps not be defined. It is not clear from
the definition, but let's use CONFIG_X86 to be sure.

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

drivers/rtc/mc146818.c

@@ -14,7 +14,7 @@
 #include <dm.h>
 #include <rtc.h>
 
-#if defined(__I386__) || defined(CONFIG_MALTA)
+#if defined(CONFIG_X86) || defined(CONFIG_MALTA)
 #include <asm/io.h>
 #define in8(p) inb(p)
 #define out8(p, v) outb(v, p)