x86: pinctrl: Add a way to get the pinctrl reg address

x86: pinctrl: Add a way to get the pinctrl reg address

At present we can query the offset of a pinctrl register within the p2sb.
For ACPI we need to get the actual address of the register. Add a function
to handle this and rename the old one to more accurately reflect its
purpose.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>