add automatic flashing of uboot

Merged Ghost User requested to merge autoflash into master

The will enable automatic flashing of the uboot firmware on PinePhones that update.

It checks if the firmware file (.bin) exists before attempting to flash. It finds the storage device, that currently has / (root) mounted and flashes the firmware to that device.

It will flash the default firmware, so if a user is using a firmware with different clock speeds, they will need to reflash it with the speed they want, since we can't check from the running OS, which they currently have flashed.

The firmware will be reflashed on each update going forward, as we can't assume that the user has all the previous uboot updates, so this will have to be done from now on.

Tested on my PinePhone UBPorts edition and my Manjaro edition

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