regulator: dt-bindings: qcom,qca6390-pmu: add more properties for wcn6855

Document two supplies that are used by this model and the optional
xo-clk signal.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20241018-sc8280xp-pwrseq-v6-1-8da8310d9564@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>