This PR adds a button to the Mainsail interface that allows the user to set the boot media to USB instead of eMMC. There is no error checking to make sure the USB drive is inserted and has a valid image and there is no way to return to eMMC if the button is pressed by mistake.
For some reason teh "set_boot_media" button does not work on first boot. But after one boot, pressing the button seems to work fine. I'll call that OK.
This PR adds a button to the Mainsail interface that allows the user to set the boot media to USB instead of eMMC. There is no error checking to make sure the USB drive is inserted and has a valid image and there is no way to return to eMMC if the button is pressed by mistake.