Mic dual complete

[oscarbailey-xmos]

UNDOCUMENTED

Single threaded mic array + tests.

Configured using the following #defines:

• MIC_DUAL_ENABLED
• MIC_DUAL_FRAME_SIZE

The mic_dual function signature:

void mic_dual_pdm_rx_decimate(
        in buffered port:32 p_pdm_mics,
        streaming chanend c_2x_pdm_mic,
        streaming chanend c_ref_audio[]);

Getting data from the mics is acheived as usual by calling mic_array_get_next_time_domain_frame.

Note: single threaded mic array is not compatible with mic_array_async_interface_enabled. (7b74de0)