ARM: dts: stm32: use internal clock for Tx for stm32mp157c-odyssey

In Odyssey board, we should use the internal clock from RCC as the
transmit clock, instead of the external clock from ETH_CLK125 pad. This
commit adds a property, st,eth-clk-sel, so that the ETH_CLK_SEL mux
selects ETH_CLK.

Signed-off-by: Heesub Shin <heesub@gmail.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/arch/arm/dts/stm32mp157c-odyssey.dts b/arch/arm/dts/stm32mp157c-odyssey.dts
index 17bcf56..53ba018 100644
--- a/arch/arm/dts/stm32mp157c-odyssey.dts
+++ b/arch/arm/dts/stm32mp157c-odyssey.dts
@@ -75,6 +75,7 @@
 	phy-mode = "rgmii-id";
 	max-speed = <1000>;
 	phy-handle = <&phy0>;
+	st,ext-phyclk;
 
 	mdio0 {
 		#address-cells = <1>;