dt-bindings: phy: Add the M31 based eUSB2 PHY bindings

On SM8750, the M31 eUSB2 PHY is being used to support USB2. Add the
binding definition for the PHY driver.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
Signed-off-by: Melody Olvera <melody.olvera@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250527-sm8750_usb_master-v6-2-d58de3b41d34@oss.qualcomm.com


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