pinctrl: lynxpoint: Relax GPIO request rules

A pin in native mode still can be requested as GPIO, though we assume
that firmware has configured it properly, which sometimes is not the case.

Here we allow turning the pin as GPIO to avoid potential issues,
but issue warning that something might be wrong.

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>