Encoder: Move initialization from M4 to M0.
Specan: Remove FFT bin static array, move to baseband handler.
Baseband: Make receiver_configuration_t private.
Baseband: Remove some dead code.
Baseband: Use actual sampling rate in DSP metrics.
Baseband: Move SGPIO DMA ack to end of interrupt.

This prevents locking up the baseband at 100% CPU utilization if the baseband handler does not complete in one baseband frame. Instead a baseband frame is dropped.
Specan: Track performance in baseband handler.
Specan: Adapt FFT code to baseband handler interface.
Baseband: Make handlers responsible for work buffers.

Handlers now create their own work buffers on the stack.
Specan: Extract into separate files.