pcm: support for audio timestamps

pcm: support for audio timestamps

add new snd_pcm_status_get_audio_htstamp() routine to
query the audio timestamps provided by the kernel.

This change provides applications with better ways
to track elapsed time. Before this patch, applications
would subtract queued samples (delay) from written samples,
resulting in a 1-2 sample error.

Also add snd_pcm_hw_params_supports_audio_wallclock_ts()
to query what the hardware supports.

TODO: check protocol compatibility?

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>