ALSA: asihpi: Add support for stream interrupt.

Some cards have a so-called low-latency mode, in which they present
a single multichannel stream with no mixing or samplerate conversion.
In this mode the card can generate an interrupt per internal processing
block (typically 32 or 64 frames)

Signed-off-by: Eliot Blennerhassett <eliot@blennerhassett.gen.nz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>