dt-bindings: net: Add missing properties used in examples

With 'unevaluatedProperties' support implemented, the following warnings
are generated in the net bindings:

Documentation/devicetree/bindings/net/qca,ar71xx.example.dt.yaml: ethernet@19000000: Unevaluated properties are not allowed ('qca,ethcfg' was unexpected)
Documentation/devicetree/bindings/net/stm32-dwmac.example.dt.yaml: ethernet@40028000: Unevaluated properties are not allowed ('reg-names', 'snps,pbl' were unexpected)
Documentation/devicetree/bindings/net/ti,cpsw-switch.example.dt.yaml: mdio@1000: Unevaluated properties are not allowed ('clocks', 'clock-names' were unexpected)
Documentation/devicetree/bindings/net/ti,k3-am654-cpsw-nuss.example.dt.yaml: mdio@f00: Unevaluated properties are not allowed ('clocks', 'clock-names' were unexpected)

Add the missing properties/nodes as necessary.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "Andreas Färber" <afaerber@suse.de>
Cc: Manivannan Sadhasivam <mani@kernel.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Cc: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Cc: "G. Jaya Kumaran" <vineetha.g.jaya.kumaran@intel.com>
Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Cc: Christophe Roullier <christophe.roullier@foss.st.com>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: netdev@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-actions@lists.infradead.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211206174153.2296977-1-robh@kernel.org