gpio: rename gpio_set_drive_single_ended() to gpio_set_config()

This commit simply renames gpio_set_drive_single_ended() to
gpio_set_config(), as the function is not specific to setting the GPIO
drive type, and will be used for other purposes in followup commits.

In addition, it moves the function above gpiod_direction_input(), as
it will be used from gpiod_direction_input().

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>