gpio: add TS-4800 fpga GPIO support

The TS-4800 GPIO driver provide support for the GPIOs available
on the Technologic Sytems board FPGA. It allows to set
direction and read/write states.

It uses the generic gpio driver.

Signed-off-by: Julien Grossholtz <julien.grossholtz@savoirfairelinux.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>