x86: broadwell: Add power-control support

Broadwell requires quite a bit of power-management setup. Add code to set
this up correctly.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Bin Meng <bmeng.cn@gmail.com>
[squashed in http://patchwork.ozlabs.org/patch/598373/

]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>