dt-bindings: net: snps, dwmac: remove tx-sched-sp property

Strict priority for the tx scheduler is by default in Linux driver, so the
tx-sched-sp property was removed in commit aed68640 ("net: stmmac:
platform: Delete a redundant condition branch").

This property is still in use in the following DT (and it will be removed
in a separate patch series):

- arch/arm64/boot/dts/freescale/imx8mp-beacon-som.dtsi
- arch/arm64/boot/dts/freescale/imx8mp-evk.dts
- arch/arm64/boot/dts/freescale/imx8mp-verdin.dtsi
- arch/arm64/boot/dts/qcom/sa8540p-ride.dts
- arch/arm64/boot/dts/qcom/sa8775p-ride.dts

There is no problem if that property is still used in the DTs above,
since, as seen above, it is a default property of the driver.

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Adam Ford <aford173@gmail.com>
Link: https://lore.kernel.org/r/20240429092654.31390-2-f.suligoi@asem.it


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