samples: basic: blinky: add mbox backend for eGPIO#1910

nordicjm merged 2 commits intonrfconnect:mainnrfconnect/sdk-zephyr:mainfrom

jaz1-nordic:mbox-backend-in-eGPIOjaz1-nordic/ncs-sdk-zephyr:mbox-backend-in-eGPIOCopy head branch name to clipboard