gpio: tc3589x: implement open drain/source callback

This makes use of the new .set_single_ended() callback to
set the GPIO line as open drain/open source using hardware.
The TC3589x can do this by either disabling the N-MOS
transistor (open drain) or the P-MOS transistor (open source)
of the output driver stage, in the first case making the signal
drive actively low and high impedance as "high" and in the second
case actively high and high impedance, which is as close to native
open drain support as we come.

Cc: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>