gpio: sch: Implement .get_direction()

It's pretty simple to implement the .get_direction() for this
chip, so let's just do it.

Cc: Denis Turischev <denis.turischev@compulab.co.il>
Cc: Daniel Krueger <daniel.krueger@systec-electronic.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>