ALSA: pcm: Introduce protocol version field to sw_params

For controlling the new fields more strictly, add sw_params.proto
field indicating the protocol version of the user-space.  User-space
should fill the SNDRV_PCM_VERSION value it's built with, then kernel
can know whether the new fields should be evaluated or not.

And now tstamp_type field is evaluated only when the valid value is
set there.  This avoids the wrong override of tstamp_type to zero,
which is SNDRV_PCM_TSTAMP_TYPE_GETTIMEOFDAY.

Signed-off-by: Takashi Iwai <tiwai@suse.de>