ASoC: mediatek: mt8183: make headset codec optional

Make headset codec optional because some variant machines may not
have an audio jack.

Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20190716032417.19015-1-tzungbi@google.com
Signed-off-by: Mark Brown <broonie@kernel.org>