arm64: xilinx: Setup default number of chipselects for zcu100

There is only one chipselect on each connector.
Define it directly in board dts file.
There should be an option to use more chipselects via gpios.
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynqmp-zcu100-revC.dts

@@ -280,11 +280,13 @@
 &spi0 { /* Low Speed connector */
 	status = "okay";
 	label = "LS-SPI0";
+	num-cs = <1>;
 };
 
 &spi1 { /* High Speed connector */
 	status = "okay";
 	label = "HS-SPI1";
+	num-cs = <1>;
 };
 
 &uart0 {