audiopolicy: Be a little smarter with auto-attach

  * The edge cases, ZOMG!
  * Instead of relying on effects to be automatically attached, let's
    just always notify userspace and send a bit more information. This
    lets the application decide if effects should be attached rather
    than relying on a hard-coded configuration file.
  * Perform the setup in getOutputForAttr, but do it on the command
    thread so we don't block the client.

OPO-593

Change-Id: I3900b349f2e895d51fa3a3dcc2de0c4bdf6dbc08