x86: ivybridge: Allow microcode to be collated

Generally the microcode is combined into a single block only (and removed
from the device tree) when there are multiple blocks. But this is not a
requirement.

Adjust the ivybridge code to avoid assuming this.

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