ARM: dts: sunxi: Add num-cs for A20 spi nodes

The spi0 controller on the A20 have up to 4 CS (Chip Select) while the
others three only have 1.
Add the num-cs property to each node.
The current driver doesn't read this property but this is useful for
downstream user of DTS (FreeBSD for example).
Signed-off-by: Emmanuel Vadot <manu@bidouilliste.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

arch/arm/boot/dts/sun7i-a20.dtsi

@@ -871,6 +871,7 @@ spi0: spi@01c05000 {
 			status = "disabled";
 			#address-cells = <1>;
 			#size-cells = <0>;
+			num-cs = <4>;
 		};
 
 		spi1: spi@01c06000 {
@@ -885,6 +886,7 @@ spi1: spi@01c06000 {
 			status = "disabled";
 			#address-cells = <1>;
 			#size-cells = <0>;
+			num-cs = <1>;
 		};
 
 		emac: ethernet@01c0b000 {
@@ -1037,6 +1039,7 @@ spi2: spi@01c17000 {
 			status = "disabled";
 			#address-cells = <1>;
 			#size-cells = <0>;
+			num-cs = <1>;
 		};
 
 		ahci: sata@01c18000 {
@@ -1079,6 +1082,7 @@ spi3: spi@01c1f000 {
 			status = "disabled";
 			#address-cells = <1>;
 			#size-cells = <0>;
+			num-cs = <1>;
 		};
 
 		pio: pinctrl@01c20800 {