dt-bindings: net: snps,dwmac: Enable burst length properties for more compatibles

With 'unevaluatedProperties' support implemented, the properties
'snps,pbl', 'snps,txpbl', and 'snps,rxpbl' are not allowed in the
examples for some of the DWMAC versions:

Documentation/devicetree/bindings/net/intel,dwmac-plat.example.dt.yaml: ethernet@3a000000: Unevaluated properties are not allowed ('snps,pbl', 'mdio0' were unexpected)
Documentation/devicetree/bindings/net/stm32-dwmac.example.dt.yaml: ethernet@5800a000: Unevaluated properties are not allowed ('reg-names', 'snps,pbl' were 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/stm32-dwmac.example.dt.yaml: ethernet@40027000: Unevaluated properties are not allowed ('reg-names', 'snps,pbl' were unexpected)
Documentation/devicetree/bindings/net/toshiba,visconti-dwmac.example.dt.yaml: ethernet@28000000: Unevaluated properties are not allowed ('snps,txpbl', 'snps,rxpbl', 'mdio0' were unexpected)

This appears to be an oversight, so fix it by allowing the properties
on the v3.50a, v4.10a, and v4.20a versions of the DWMAC.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Jose Abreu <joabreu@synopsys.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20211206174147.2296770-1-robh@kernel.org