arm: zynq: dts: add spi flash node to zedboard

Add a flash node to fix the detection of the memory IC.
With the changes introduced with commit 8fee8845e7
("enf_sf: reuse setup_flash_device instead of open coding it")
the SPI speed is now read from device-tree or a default value
is applied. This replaced the old behavior of setting the
SPI speed to CONFIG_ENV_SPI_MAX_HZ.

As this board didn't have a flash node, the default value
was applied to the SPI speed, producing an error when probing
the flash memory (speed too slow).

Signed-off-by: Luis Araneda <luaraneda@gmail.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynq-zed.dts

@@ -51,6 +51,13 @@
 &qspi {
 	u-boot,dm-pre-reloc;
 	status = "okay";
+	num-cs = <1>;
+	flash@0 {
+		compatible = "spansion,s25fl256s", "spi-flash";
+		reg = <0>;
+		spi-max-frequency = <30000000>;
+		m25p,fast-read;
+	};
 };
 
 &sdhci0 {