gpio: pxa: disable pinctrl calls for MMP_GPIO

Similarly to PXA3xx and MMP2, pinctrl-single isn't capable of setting
pin direction on MMP either.

Fixes: a770d946 ("gpio: pxa: add pin control gpio direction and request")
Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>