gpio: sama5d2-piobu: Set proper output level for direction_output

Set proper output level base on the argument of direction_output.
Also remove sama5d2_piobu_set_direction() as there is only one caller
now.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>