uboot-imx

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>