FMUv5: Swap debug and PX4 IO serial ports to avoid DMA channel issues

[LorenzMeier]

This is necessary to be able to use DMA on the IO link. We free one channel by disabling DMA entirely on the debug console.

[LorenzMeier]

@PX4BuildBot Rebase.

[PX4BuildBot]

Hey! I'm GitMate.io! This pull request is being rebased automatically. Please DO NOT push while rebase is in progress or your changes would be lost permanently ⚠️

[PX4BuildBot]

Automated rebase failed! Please rebase your pull request manually via the command line.

Reason:

Command: git rebase base/master

Exit Code: 128

Cause:

.git/rebase-apply/patch:86: trailing whitespace.
CheckOptions:    
.git/rebase-apply/patch:2671: trailing whitespace.
To install doxygen: 
.git/rebase-apply/patch:2683: trailing whitespace.
The html file index.html should be in doc/html unless you changed the output directory. 
.git/rebase-apply/patch:2698: trailing whitespace.
Run the wizard to generate the documentation. 
.git/rebase-apply/patch:3940: trailing whitespace.
The [PX4 User Guide](https://docs.px4.io/en/) explains how to assemble [supported vehicles](https://docs.px4.io/en/airframes/airframe_reference.html) and fly drones with PX4. 
warning: squelched 993 whitespace errors
warning: 998 lines add whitespace errors.
error: Failed to merge in the changes.

[LorenzMeier]

I've updated the pinout:

https://docs.google.com/spreadsheets/d/1-n0__BYDedQrc_2NHqBenG1DNepAgnHpSGglke-QQwY/edit#gid=912976165