In BXT-P A0, HD-Audio DMA requests is later than expected,
and makes an audio stream sensitive to system latencies when
24/32 bits are playing.
Adjusting threshold of DMA fifo to force the DMA request
sooner to improve latency tolerance at the expense of power.

v2: move Intel specific code to hda_intel.c
Signed-off-by: NLu, Han <han.lu@intel.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>