ASoC: dt-bindings: Add WCD9335 MBHC specific properties

This patch add new bindings required to support MBHC
(Multi Button Headset Control) block in the codec.
This block is used for jack insert/removal detection,
headset type detection and 8 button press/release events.

All these properties are very much specific to board.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>