ARM: shmobile: silk: Move SPI FLASH partitions to subnode

As of commits 5cfdedb7b9a0fe38 ("mtd: ofpart: move ofpart partitions to a
dedicated dt node") and fe2585e9c29a650a ("doc: dt: mtd: support partitions
in a special 'partitions' subnode"), having partitions as direct subnodes
of an mtd device is discouraged. Hence move the SPI FLASH partitions to a
"partitions" subnode.

Based on similar work for the koelsch board by Geert Uytterhoeven.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7794-silk.dts

@@ -194,8 +194,6 @@
 	status = "okay";
 
 	flash@0 {
-		#address-cells = <1>;
-		#size-cells = <1>;
 		compatible = "spansion,s25fl512s", "jedec,spi-nor";
 		reg = <0>;
 		spi-max-frequency = <30000000>;
@@ -205,19 +203,24 @@
 		spi-cpha;
 		m25p,fast-read;
 
-		partition@0 {
-			label = "loader";
-			reg = <0x00000000 0x00040000>;
-			read-only;
-		};
-		partition@40000 {
-			label = "user";
-			reg = <0x00040000 0x00400000>;
-			read-only;
-		};
-		partition@440000 {
-			label = "flash";
-			reg = <0x00440000 0x03bc0000>;
+		partitions {
+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			partition@0 {
+				label = "loader";
+				reg = <0x00000000 0x00040000>;
+				read-only;
+			};
+			partition@40000 {
+				label = "user";
+				reg = <0x00040000 0x00400000>;
+				read-only;
+			};
+			partition@440000 {
+				label = "flash";
+				reg = <0x00440000 0x03bc0000>;
+			};
 		};
 	};
 };