x86: Add a script to process Intel microcode files

Intel delivers microcode updates in a microcode.dat file which must be
split up into individual files for each CPU. Add a tool which performs
this task. It can list available microcode updates for each model and
produce a new microcode update in U-Boot's .dtsi format.

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