dt-bindings: phy: Add PHY_TYPE_USXGMII definition

Add definition for USXGMII phy type.

Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Swapnil Jakhade <sjakhade@cadence.com>
Signed-off-by: Roger Quadros <rogerq@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220628122255.24265-3-rogerq@kernel.org


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