serial: mctrl_gpio: Drop support for out1-gpios and out2-gpios

The OUT1 and OUT2 pins present on some legacy UARTs are basically GPIOs.
It doesn't make much sense to emulate GPIOs using other GPIOs, hence
drop support for that.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Richard Genoud <richard.genoud@gmail.com>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>