Feature request: sd:/bootorder.txt

[PlugNPush]

Instead of hardcoding boot.firm in the main.c file, I think it would be a good idea to add a possibility to bypass it using a text file (ex: bootorder.txt) which would be able to provide a list of 1 firm file per line and detect the first one available to boot it.

This would be especially useful for using BAX firms without messing around with ordinary boot.firm locations to allow smoother updates.

Right now, I made a fork of B9S to support BAX in a hardcoded way.
I think it would be great to officially adopt this, but using a text file to specify which firm to load first and provide some flexibility.

Of course, it would always default to the hardcoded boot.firm file if no other firm is found, wether a bootorder.txt file is present or not.

[PlugNPush]

I would happily provide a PR for this if I get some sort of approval for the feature itself.

[PlugNPush]

I actually did not wait for the approval, I am going to use it anyways for my own use :)