ASoC: rt5677: Load firmware via SPI using delayed work

The firmware rt5677_elf_vad is an ELF binary obtained from
request_firmware(). Sections of the ELF are loaded to
the DSP via SPI. A model (e.g. en_us.mmap) can optionally be
loaded to the DSP at RT5677_MODEL_ADDR to overwrite the
baked-in model in rt5677_elf_vad.

Then we switch to DSP mode, load firmware, and let DSP run.
When a hotword is detected, an interrupt is fired and
rt5677_irq() is called. When 'DSP VAD Switch' is turned off,
the codec is set back to normal mode.

The kcontrol 'DSP VAD Switch' is automatically enabled/disabled
when the hotwording PCM stream is opened/closed.

Signed-off-by: Ben Zhang <benzh@chromium.org>
Signed-off-by: Curtis Malainey <cujomalainey@chromium.org>
Link: https://lore.kernel.org/r/20191106011335.223061-2-cujomalainey@chromium.org
Signed-off-by: Mark Brown <broonie@kernel.org>