soc: nrf: remove use of NRF_GPIO_PIN_MAP

Commit 7cdd10bf
("soc: arm: nordic: add NRF_DT_GPIOS_TO_PSEL_BY_IDX") added a use of
NRF_GPIO_PIN_MAP to soc_nrf_common.h without including the relevant
HAL header where it is defined, hal/nrf_gpio.h.

Unfortunately, including that header causes even more problems, since
it causes undefined NRFX_ASSERT() calls to appear elsewhere in the
tree.

It's not really worth bothering to use this macro. Just expand it
inline instead.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>