ss_force is a debugging option to force a certain single stream
tx mode. It's not useful if it gets reset after tx idle. Fix that.
While at it also make sure any code touching ss_force will only
get compiled if debugfs support is configured.
Signed-off-by: NEyal Shapira <eyalx.shapira@intel.com>
Reviewed-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NEmmanuel Grumbach <emmanuel.grumbach@intel.com>