riscv: dts: renesas: Clean up dtbs_check W=1 warning due to empty phy node

dtbs_check w/ W=1 complains:

    Warning (unit_address_vs_reg): /soc/ethernet@11c20000/ethernet-phy@7: node has a unit name, but no reg or ranges property
    Warning (avoid_unnecessary_addr_size): /soc/ethernet@11c20000: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

The ethernet@11c20000 node is guarded by an `#if (!SW_ET0_EN_N)` in
rzg2ul-smarc-som.dtsi, where the phy child node is added. In
rzfive-smarc-som.dtsi, the ethernet node is marked disabled & the
interrupt properties are deleted from the phy child node. As a result,
the produced dts looks like:

    ethernet@11c20000 {
	    compatible = "renesas,r9a07g043-gbeth",
	    		 "renesas,rzg2l-gbeth";
	    /* snip */
	    #address-cells = <1>;
	    #size-cells = <0>;
	    status = "disabled";

	    ethernet-phy@7 {
	    };
    };

Adding a corresponding `#if (!SW_ET0_EN_N)` around the node in
rzfive-smarc-som.dtsi avoids the complaint, as the empty child node is
not added:

    ethernet@11c20000 {
	    compatible = "renesas,r9a07g043-gbeth",
	    		 "renesas,rzg2l-gbeth";
	    /* snip */
	    #address-cells = <1>;
	    #size-cells = <0>;
	    status = "disabled";
    };
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230712-squealer-walmart-9587342ddec1@wendySigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

arch/riscv/boot/dts/renesas/rzfive-smarc-som.dtsi

@@ -22,6 +22,7 @@ &dmac {
 	status = "disabled";
 };
 
+#if (!SW_ET0_EN_N)
 &eth0 {
 	status = "disabled";
 
@@ -30,6 +31,7 @@ phy0: ethernet-phy@7 {
 		/delete-property/ interrupts;
 	};
 };
+#endif
 
 &eth1 {
 	status = "disabled";