Revert "Revert "ALSA backend: separate flags for is-running and should-be-running""

sorry, c/p error
This reverts commit 9658b77327c21d5748604b882f67c5004ffd10ad.
Revert "add API to query a processor's frozen state."

Theoretically one could alter the plugins after a delivery even on a
frozen track. ..or even change settings, the ordering and add/remove
plugins after the frozen part of a track.

We won't go there. Frozen is frozen. this API is not needed after all.

This reverts commit a771dea20332bf31162ccb13a518e0348b441dd1.