x86: ich6-gpio: Move setup_pch_gpios() to board support codes

Movie setup_pch_gpios() in the ich6-gpio driver to the board support
codes, so that the driver does not need to know any platform specific
stuff (ie: include the platform specifc chipset header file).

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