uart: minor docs improvements

[JurajSadel]

First driver of #3180. This doesn't change logic of the driver just reshuffle some functions.
I think I will work on one driver at a time to avoid ugly rebasing of multiple files.

[bjoernQ]

The functions not sorted for me

And the impl blocks are also not really sorted

(Blocking, Async, Any, Blocking, Async)

Maybe we should define a sorting order

[bugadani]

We should maybe also merge the separate Blocking and Async blocks, we don't need multiple of them.

[MabezDev]

I could have been a bit more clear in the original issue, sorry about that!

• I think we should have only 3 impls blocks in the docs (ignoring trait impls obviously)
  • Blocking (should go first, as it's the entry point to creating most drivers)
  • Async
  • impl for Both

Re grouping inside the blocks, I think I agree with @bugadani's point (#3216 (comment)). This is more inline with how upstream Rust does it, for example: https://doc.rust-lang.org/core/primitive.i32.html#method.strict_add is placed next to the other add functions. Let's just try and organize it so that at the very least the first few items we see for a driver are stable, if possible please :D.

I think I will work on one driver at a time to avoid ugly rebasing of multiple files.

Good idea!

[bjoernQ]

LGTM

[MabezDev]

LGTM, thanks for updating the guidelines too!