pinctrl: baytrail: Factor out byt_gpio_force_input_mode()

There is a piece of code that it being used at least twice.
Factor it out.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>