dt-bindings: phy: ocelot-serdes: convert to YAML

Convert the phy-ocelot-serdes device tree binding to the new YAML format.

Additionally, add the file to MAINTAINERS since the original file didn't
exist.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220911163715.4036144-2-colin.foster@in-advantage.com


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