ASoC: rt5677: Support DSP function for VAD application

The ALC5677 has a programmable DSP, and there is a SPI that is dadicated for DSP
firmware loading. Therefore, the patch includes a SPI driver for writing the DSP
firmware. The VAD(Voice Activaty Detection) has be implemented and use the DSP to
recognize the key phase.

Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>