dt-bindings: net: marvell,pp2: convert to json-schema

Convert the marvell,pp2 bindings from text to proper schema.

Move 'marvell,system-controller' and 'dma-coherent' properties from
port up to the controller node, to match what is actually done in DT.

Rename all subnodes to match "^(ethernet-)?port@[0-2]$" and deprecate
port-id in favour of 'reg'.

Signed-off-by: Michał Grzelak <mig@semihalf.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>