Add more UART baud rates

[lippit]

There were only a few baud rates supported by CPCd, and not all of them were compatible with all host devices. Adding more baud rates improves compatability.

[yacinbm]

Hi @lippit thanks for your contribution!

These changes seem reasonable to me.

@aautotte the only thing I would change is to add a check to enforce users to use hardware flow control above 921600, otherwise interrupt latency can start causing issues.