Fetch submodules lazily

[dhalbert]

Instead of having to do a slow make fetch-submodules at the top level after cloning circuitpython, fetch the submodules lazily. Fetch the submodules for a particular port only when a build is done in that port directory.

... working on this.

[bill88t]

I feel like make fetch-submodules shouldn't be removed.
It's nice to be able to run one command to prepare the local repo so that you can go offline.

But seperating it into auto triggers for every port sounds like a great idea.

[joshua-beck-0908]

That would be nice. I just wait a long time for every submodule just to change one line of an esp32 board definition. Then the esp-idf build failed anyway. 😅