ASoC: AMD: Support headset button on Stoney DA7219

Adds headset button support.

TEST=Tested Volume UP/Down, Play/Pause functionality

Signed-off-by: Akshu Agrawal <akshu.agrawal@amd.com>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>