dt-bindings: net: orion-mdio: Convert to JSON schema

Convert the marvell,orion-mdio binding to JSON schema.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220505210621.3637268-1-chris.packham@alliedtelesis.co.nz


Signed-off-by: Jakub Kicinski <kuba@kernel.org>