dt-bindings: phy: Remove Cadence MHDP PHY dt binding

Remove the Cadence MHDP PHY bindings. The binding is added
in next commit in YAML format. It is renamed to adopt
torrent nomenclature.
This will not affect ABI as the driver has never been functional,
and therefore do not exist in any active use case.

Signed-off-by: Yuti Amonkar <yamonkar@cadence.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>