Bringing in tm4c129 support.

[dtwood]

I won’t be able to review this in much detail until I’m home from work, but if you want to preserve the history of the 129x repo, it should be possible to do something like this:

git remote add https://github.com/dtwood/tm4c129x-hal 129x
git remote update
git checkout -b 129x
git reset —hard 129x/master
mv * tm4c129x-hal
git commit -a
git checkout adding_129_support
git merge . 129x —allow-unrelated-histories

It would probably be helpful for me when trying to merge back in the Ethernet (and svd2rust ephy) support if the history was preserved.