dt-bindings: phy: Convert img,pistachio-usb-phy to DT schema

Convert the Imagination Pistachio USB PHY binding to DT schema format.
It's a straight forward conversion.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250607212531.742082-1-robh@kernel.org


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