command: pass optional baudrate argument to swo_init in Manchester mode

[Misaka0x2730]

Detailed description

I'm working on a custom platform, and because my Manchester decoding implementation is based on the RP2040 PIO, I need to pass the incoming signal's baud rate to the device in Manchester mode as well.
I believe this change will not affect other platforms, since the baudrate argument in the swo command is optional, and in the general swo_init implementation, the baudrate is only used in UART mode.

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