hw: add option to specify dynamic DAPM routing to apply when the plugin is opened #192
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The kernel's sound soc subsystem has a DAPM functionality, which makes complex audio routing easy, and most of it is done inside the kernel. However, in the case of dynamic routing (when there is a multiplexer in the signal path), the multiplexer is exposed as an enum MIXER control which must be set from userspace. As the selection of these controls directly influences what audio path is captured/played, the sensible thing to do is to create multiple HW plugins in the ALSA conf, each referring to the same HW device number, but with different routing parameters.