I've looked at two x86 drivers in drivers/gpiolib (cs5535 and langwell) and
there's no treatment of ACPI in either of them. Since SCH is defined by Intel
as "embedded" product, having a GPIO driver for it seems logical even despite
problems you mention.
I believe that Langwell is used only in products without an ACPI BIOS.
Poulsbo, OTOH, is used in zillions of netbooks running Windows XP.
I don't know what a cs5535 is.
Len Brown, Intel Open Source Technology Center