ASoC: rt5514: expose Hotword Model control

This change exposes mixer control 'Hotword Model' for switching
hotword model in runtime. This new function requires updated
firmware to load hotword model at address 0x4ff80000.

Signed-off-by: Hsin-Yu Chao <hychao@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>