Missing feature: shutdown

[xross]

This component doesn't include provision shutdown

The precludes support for sample rate change.

[ed-xmos]

Note a version with shutdown has been implemented here https://github.com/ed-xmos/lib_xua/tree/feature/mic_array_v5_sr_change which overrides various members of the classes to support this feature. However we may wish to make this available in the core lib rather than having to override each time.