x86: broadwell: Add a pinctrl driver

GPIO pins need to be set up on start-up. Add a driver to provide this,
configured from the device tree.

The binding is slightly different from the existing ICH6 binding, since that
is quite verbose. The new binding should be just as extensible.

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

x86: gpio: add pinctrl support from the device tree

Every pin can be configured now from the device tree. A dt-bindings
has been added to describe the different property available.

Change-Id: I1668886062655f83700d0e7bbbe3ad09b19ee975
Signed-off-by: Gabriel Huau <contact@huau-gabriel.fr>
Acked-by: Simon Glass <sjg@chromium.org>