dt-bindings: mux: add optional regulator binding to gpio mux

dt-bindings: mux: add optional regulator binding to gpio mux

On some platforms to minimise pop and click during switching between
CTIA and OMTP headset an additional HiFi Mux Switch is used. Most common
case is that this switch is switched on by default, but on some
platforms this needs a regulator enable. One such platform is Lenovo
T14s.

Adds required bindings in gpio-mux to add such optional regulator.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250327100633.11530-2-srinivas.kandagatla@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>