ARM: dts: stm32: remove "snps,en-tx-lpi-clockgating" property

Whether the MII transmit clock can be stopped is primarily a property
of the PHY (there is a capability bit that should be checked first.)
Whether the MAC is capable of stopping the transmit clock is a separate
issue, but this is already handled by the core DesignWare MAC code.

As commit "net: stmmac: stm32: use PHY capability for TX clock stop"
adds the flag to use the PHY capability, remove the DT property that is
now unecessary.

Cc: Samin Guo <samin.guo@starfivetech.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tsIUA-005vGX-8A@rmk-PC.armlinux.org.uk
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

arch/arm/boot/dts/st/stm32mp151.dtsi

@@ -1781,7 +1781,6 @@
 				st,syscon = <&syscfg 0x4>;
 				snps,mixed-burst;
 				snps,pbl = <2>;
-				snps,en-tx-lpi-clockgating;
 				snps,axi-config = <&stmmac_axi_config_0>;
 				snps,tso;
 				access-controllers = <&etzpc 94>;