alsa: get avail, delay, timestamps in a single kernel call

alsa: get avail, delay, timestamps in a single kernel call

Refactor code to fetch avail, delay and timestamp values
in a single call to snd_pcm_status().
The information reported is exactly the same as before,
however it is extracted in a more atomic manner to
improve timer-based scheduling.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>