dt-bindings: phy: qcom-qusb2: Document SDM660 compatible

Support for the SDM630/660 series of SoCs was added to the driver:
document the qcom,sdm660-qusb2-phy compatible here.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210114174718.398638-3-angelogioacchino.delregno@somainline.org


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