drivers: gpio: nrfx: extend pin retain to every pin

The usage of nrf_gpio_port_retain_disable/_enable, in cases where
the soc pins support retention, every pin must be
retained/unretained regardless of what power domain the pad is in.

This patch ensures retain is applied to all pins in all domains by
the gpio_nrfx device driver, not only pins specifically in the
fast_active_1 domain. Without this patch, pinctrl will correctly
retain pins, while gpio_nrfx will fail to unretain them when
again.

We no longer check the output state either, which was passed with
the flags arg of gpio_nrfx_gpd_retain_set() so this arg has been
removed.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>