ARC: [plat-hsdk]: Add missing FIFO size entry in GMAC node

Add the binding for RX/TX fifo size of GMAC node.

Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Tested-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Acked-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/boot/dts/hsdk.dts

@@ -196,6 +196,9 @@ gmac: ethernet@8000 {
 			mac-address = [00 00 00 00 00 00]; /* Filled in by U-Boot */
 			dma-coherent;
 
+			tx-fifo-depth = <4096>;
+			rx-fifo-depth = <4096>;
+
 			mdio {
 				#address-cells = <1>;
 				#size-cells = <0>;