ARM: dts: microchip: sama7g5: Add RMII ext refclk flag

The REFCLK for the RMII interface is provided by an extrenal source.

This flag matches the change in the macb driver to determine the REFCLK
source.

Signed-off-by: Ryan Wanner <Ryan.Wanner@microchip.com>
Signed-off-by: NipaLocal <nipa@local>

Author: ryan-wanner

arch/arm/boot/dts/microchip/at91-sama7g5ek.dts

@@ -542,6 +542,7 @@
 	phy-mode = "rmii";
 	nvmem-cells = <&eeprom1_eui48>;
 	nvmem-cell-names = "mac-address";
+	cdns,refclk-ext;
 	status = "okay"; /* Conflict with pdmc0. */
 
 	ethernet-phy@0 {