auhal: Support for nonstandard audio channel mappings with holes inside

Some pro users have complex channel mapping which holes inside, i.e. 3->left 4->right 5->left surround 6->left surround 7->center 8->sub.

This means that the first channels, or some channels in between are unused. Nevertheless, auhal only outputs from channel 1 onwards, after remapping.

To fix this, we would need to have a custom channel remapping algorithm to fill up these holes with 0 values so that all channels from 1 to maxnum get data.

See discussion in #10125 (closed).