x86: Intel MID platforms has no microcode update

There is no microcode update available for SoCs used on Intel MID
platforms.

Use conditional to bypass it.

Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>