add devfs support.  when devfs is enabled, sysctl hw.sndunit is used to set which sound unit the /dev/{dsp,mixer,dspW,audio} links point at.  this can also be set from the loader.
add devfs support.  when devfs is enabled, sysctl hw.sndunit is used to set
which sound unit the /dev/{dsp,mixer,dspW,audio} links point at.  this can
also be set from the loader.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase