dt-bindings: mfd: ocelot: add ethernet-switch hardware support

The main purpose of the Ocelot chips are the Ethernet switching
functionalities. Document the support for these features.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com> # regression
Signed-off-by: Jakub Kicinski <kuba@kernel.org>