SPI, I2C and UART should have API to enable DMA usage

[jeez]

There should be way for users to give a "hint" for these modules that a DMA transfer is preferred.
I call it a hint since a DMA transaction is not always available. The underlying controller / platform might not support it.

It is also not a good idea to just use DMA by default where available because usually this feature increases the application footprint considerably.

[bdilly]

We need to discuss it and see if it's relevant given our target audience.
We must balance how much low level control we want to allow avoiding to get to a complex / bloated API for newcomers.