dt-bindings: phy: Add lan966x-serdes binding

Document the lan966x ethernet serdes phy driver bindings.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20211116100818.1615762-2-horatiu.vultur@microchip.com


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