Basic support for the GPIO available on the SBC610 VPX Single Board Computer
from GE Fanuc (PowerPC MPC8641D).

This patch adds basic support for the GPIO in the devices I/O FPGA, the GPIO
functionality is exposed through the AFIX pins on the backplane, unless used
by an AFIX card.

This code currently does not support switching between totem-pole and
open-drain outputs (when used as outputs, GPIOs default to totem-pole).
The interrupt capabilites of the GPIO lines is also not currently supported.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>