gpio: Add GPIO support for the ACCES PCI-IDIO-16

The ACCES PCI-IDIO-16 device provides 32 lines of digital I/O (16 lines
of optically-isolated digital inputs for AC and DC control signals, and
16 lines of solid state switch digital outputs). An interrupt is
generated when any of the inputs change state (low to high or high to
low). Input filter control is not supported by this driver, and input
filters are deactivated by this driver.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>