gpio: Add PMIC GPIO block support

Moorestown has PMIC chip which contains GPIO blocks. The PMIC chip is
connected to Langwell by SPI interface. So this GPIO driver will be regarded
as SPI GPIO expander though the actual GPIO access is through IPC and SRAM.
The SPI master contoller will probe this device driver by parsing SPIB table.

Cleaned up for new IPC, GPE removed and some printk and other tidying by
Alan Cox. Fixes for points noted by Matthew Garrett

Signed-off-by: Alek Du <alek.du@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>