ath79: reduce 'nvmem-cells' definitions on ALFA Network QCA9531 boards

All the QCA9531 based boards from ALFA Network are based on the same
design and share a common DTSI: 'qca9531_alfa-network_r36a.dtsi'.

Instead of defining 'nvmem-cells' for the MAC address in every device's
DTS, move definition to the common DTSI file.

Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>

target/linux/ath79/dts/qca9531_alfa-network_n2q.dts

@@ -120,13 +120,3 @@
 &pcie0 {
 	status = "okay";
 };
-
-&art {
-	compatible = "nvmem-cells";
-	#address-cells = <1>;
-	#size-cells = <1>;
-
-	macaddr_art_1002: macaddr@1002 {
-		reg = <0x1002 0x6>;
-	};
-};

target/linux/ath79/dts/qca9531_alfa-network_pi-wifi4.dts

@@ -86,13 +86,3 @@
 		#trigger-source-cells = <0>;
 	};
 };
-
-&art {
-	compatible = "nvmem-cells";
-	#address-cells = <1>;
-	#size-cells = <1>;
-
-	macaddr_art_1002: macaddr@1002 {
-		reg = <0x1002 0x6>;
-	};
-};

target/linux/ath79/dts/qca9531_alfa-network_r36a.dts

@@ -81,13 +81,3 @@
 		debounce-interval = <60>;
 	};
 };
-
-&art {
-	compatible = "nvmem-cells";
-	#address-cells = <1>;
-	#size-cells = <1>;
-
-	macaddr_art_1002: macaddr@1002 {
-		reg = <0x1002 0x6>;
-	};
-};

target/linux/ath79/dts/qca9531_alfa-network_r36a.dtsi

@@ -86,6 +86,14 @@
 				label = "art";
 				reg = <0x070000 0x010000>;
 				read-only;
+
+				compatible = "nvmem-cells";
+				#address-cells = <1>;
+				#size-cells = <1>;
+
+				macaddr_art_1002: macaddr@1002 {
+					reg = <0x1002 0x6>;
+				};
 			};
 
 			partition@80000 {