gpio: kona: Add Kona gpio driver

Add support for the Kona GPIO controller found on Broadcom mobile SoCs.

Signed-off-by: Darwin Rambo <drambo@broadcom.com>
Reviewed-by: Steve Rae <srae@broadcom.com>
Reviewed-by: Markus Mayer <markus.mayer@linaro.org>
Reviewed-by: Tim Kryger <tkryger@linaro.org>