Input: improve usage of gpiod API

Since 39b2bbe3

 (gpio: add flags argument to gpiod_get*() functions)
which appeared in v3.17-rc1, the gpiod_get* functions take an additional
parameter that allows to specify direction and initial value for
output. Simplify drivers accordingly.

Note that in the case of the drv260x driver error checking is more
strict now because -ENOSYS is reported to the caller now. But this
should only be returned if GPIOLIB is disabled which shouldn't happen as
the driver depends on GPIOLIB.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>