ALSA: rme96: Add pcm stream synchronization

The hardware does support synchronized start/pause/stop of pcm streams,
so there is no reason not to add that feature after more than ten years.

Some minor coding style / white space fixes in the surroundings of the
changes.
Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>