USART channel selection for serial line debugging

When General/Debug is activated, there is a new option for USART channel selection. The selected channel is compared against the MCU capabilities, i. e. you can only select USART 1 when the MCU has it.

This change has implications with the m4 files for beteigeuze and antares* in pinning/hardware, as they have an entry selecting USART 1 for debugging. This line has been removed, as the channel will now be delivered through menuconfig and the associated profile. This requires rebuilding these profiles and manually changing the USART selection to 1.

As I can not estimate the implications of profile regeneration, profiles should be commited later, after the ccode change is accepted.