ASoC: wm_adsp: Specifically propagate voice trigger event to caller

The DSP uses an IRQ to indicate data is available on the compressed
stream. For voice trigger use-cases the first such IRQ can be considered
an indication that the user has spoken the key phrase triggering the
firmware. Provide a means for the ADSP code to communicate back to the
calling driver whether an IRQ should be considered as trigger event or
not.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>