arm64: zynqmp: Used fixed-partitions for QSPI in k26

Using fixed partitions is recommended way how to describe QSPI. Also add
label for qspi flash memory to be able to reference it in future.
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/7368dc772d8dc29477a880ac2065e2ecb98cf3f5.1684767562.git.michal.simek@amd.com

arch/arm64/boot/dts/xilinx/zynqmp-sm-k26-revA.dts

@@ -127,6 +127,12 @@ spi_flash: flash@0 { /* MT25QU512A */
 		spi-tx-bus-width = <4>;
 		spi-rx-bus-width = <4>;
 		spi-max-frequency = <40000000>; /* 40MHz */
+
+		partitions {
+			compatible = "fixed-partitions";
+			#address-cells = <1>;
+			#size-cells = <1>;
+
 			partition@0 {
 				label = "Image Selector";
 				reg = <0x0 0x80000>; /* 512KB */
@@ -210,6 +216,7 @@ partition@22A0000 {
 				reg = <0x22A0000 0x1d60000>; /* 29.375 MB */
 			};
 		};
+	};
 };
 
 &sdhci0 { /* MIO13-23 - 16GB emmc MTFC16GAPALBH-IT - U133A */