Added basic mods for atmega16u2

[zacharytomlinson]

make atmega16u2
-e SVD2RUST atmega16u2
error: a value is required for '-i ' but none was supplied

[Rahix]

Hi,

I think the problem is that your ATDF is called atmega16U2 instead of atmega16u2...

[Rahix]

I pushed commit 5a58673 ("make: Fix make continuing when the ATDF source file is missing") to have make error out instead of svd2rust when this happens. But the error message is still not great due to my make magic not being good enough...

[zacharytomlinson]

Jesus your right.... That's the stupidest mistake I've made in at least the last 12 minutes lol. I changed the filename and now it is building. How would you prefer for me to clean up? Mark the issue complete, close this draft PR and open a new one, or just update this PR?

[Rahix]

Well, the error message could have been way more clear - there's nothing hinting at a file not being found... So don't be too hard on yourself ^^

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Usually, it would have been just fine to continue with this PR, and then mark it as ready for review once you are done. But you can also open a new one, don't worry :)

[zacharytomlinson]

I am going to do a once-over of the patch to make sure the basics are all in there and there are no glaring issues and then I will open a new one!