Multiple consoles support.

[zephyrbot]

Reported by Michał Kruszewski:

I think it would be nice if multiple console support would be possible.
For example, I can imagine using it when developing some application on Zephyr.
It is really convenient to log kernel information and application information to separate files.
The other example I can think of is logging information with different severity. For example, Warnings and Errors to one console and statistics information to another one.
With RTT it should be quite easy to implement and making it configurable via Kconfig does not look like impossible.

(Imported from Jira ZEP-2284)

[nashif]

this is already implemented and possible.