gpio: silabs gecko: Use macro for port initialization
gpio: silabs gecko: Use macro for port initialization

This removes a lot of copy-and-paste.

Signed-off-by: Christian Taedcke <1d7d3458c4d94e1013a9872dbd5fe0865ba6a124@taedcke.com>

zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr