GPIO PHY reset on Rev C3 boards
This incorporates Tim Small's recommended delay value of 280us.
https://forum.digikey.com/t/ethernet-device-is-not-detecting-on-ubuntu-20-04-lts-on-bbg/19948/71 https://forum.beagleboard.org/t/recognizing-a-beaglebone-black-rev-c3-board/31249/11