dt-bindings: phy: Convert Cadence DPHY binding to yaml

Convert Cadence DPHY binding to YAML. While here, make the clocks
optional and add an optional "power-domains" property.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>