ASoC: nau8821: Add headset button detection

This patch adds the function of headphone button detection,
Button detection will be enabled if the device tree
has a key_enable property.

Signed-off-by: Seven Lee <wtli@nuvoton.com>
Link: https://lore.kernel.org/r/20220627032959.3442064-1-wtli@nuvoton.com
Signed-off-by: Mark Brown <broonie@kernel.org>