pinctrl: single: config: enable the pin's input

It enables / disables the input buffer. As explained in the description
of 'enum pin_config_param' this does not affect the pin's ability to
drive output.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Acked-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20210602150420.18202-1-dariobin@libero.it
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>