dt-bindings: soundwire: qcom: document optional wake irq

Wake IRQ is optional interrupt that can be wired up on SoundWire controller
instances like RX path along with MBHC(Multi Button Headset connection).
Document this in bindings.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20220228172528.3489-3-srinivas.kandagatla@linaro.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>