linux-phytec-ti

gpio: sch311x: Implement open drain support

The chip has a bit for controlling open drain, and it is
easy to implement the callback to support open drain when
needed, so let's implement it.

Cc: Bruno Randolf <br1@einfach.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>