ARM: dts: stm32: Enable MAC TX clock gating during TX low-power mode on stm32mp15

When there is no activity on ethernet phy link, the ETH_GTX_CLK is cut.
Signed-off-by: Christophe Roullier <christophe.roullier@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32mp151.dtsi

@@ -1377,6 +1377,7 @@ ethernet0: ethernet@5800a000 {
 			st,syscon = <&syscfg 0x4>;
 			snps,mixed-burst;
 			snps,pbl = <2>;
+			snps,en-tx-lpi-clockgating;
 			snps,axi-config = <&stmmac_axi_config_0>;
 			snps,tso;
 			status = "disabled";