gpio: add TB10x GPIO driver

The GPIO driver for the Abilis Systems TB10x series of SOCs based on ARC700
CPUs. It supports GPIO control and GPIO interrupt generation. This driver
works in conjunction with the TB10x pinctrl driver.

Signed-off-by: Sascha Leuenberger <sascha.leuenberger@abilis.com>
Signed-off-by: Christian Ruppert <christian.ruppert@abilis.com>
Acked-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>