Do not enable UART DMA flags unconditionally

[Windfisch]

Fixes #334

I have not tested that code, though, so proceed with caution :)

[Windfisch]

Updated as per #334 (comment).

[Windfisch]

Renamed serial-dma split and i2c free functions to release as per #334 (comment).

[TheZoq2]

Thanks for the PR! I pointed out a few muts which cause warnings, other than that I think this is ready to merge (possibly after testing on hw)

[burrbull]

cc @TeXitoi

[TeXitoi]

@burrbull you want acces right to this repo?

[burrbull]

@burrbull you want acces right to this repo?

It would be great.

[TeXitoi]

I can't find how to add you to the stm32f1 team, looks like I don't have the right or I can't find the settings

[adamgreig]

Previously only @therealprof was a maintainer for the stm32f1 team, but I've added you as well @TeXitoi, so you should be able to add new team members now.

[TeXitoi]

Thanks, @burrbull added.

[burrbull]

Thanks.