spi: dt-bindings: spi-controller: explicitly require #address-cells=<0> for slave mode

scripts/dtc/checks.c:
if (get_property(node, "spi-slave"))
	spi_addr_cells = 0;
if (node_addr_cells(node) != spi_addr_cells)
	FAIL(c, dti, node, "incorrect #address-cells for SPI bus");
if (node_size_cells(node) != 0)
	FAIL(c, dti, node, "incorrect #size-cells for SPI bus");

The above code in check_spi_bus_bridge() require that the number of address
cells must be 0. So we should explicitly declare "#address-cells = <0>".

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20201013160845.1772-4-thunder.leizhen@huawei.com
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/spi/spi-controller.yaml

@@ -20,7 +20,7 @@ properties:
     pattern: "^spi(@.*|-[0-9a-f])*$"
 
   "#address-cells":
-    const: 1
+    enum: [0, 1]
 
   "#size-cells":
     const: 0
@@ -52,11 +52,19 @@ properties:
     description:
       The SPI controller acts as a slave, instead of a master.
 
-oneOf:
-  - required:
-      - "#address-cells"
-  - required:
-      - spi-slave
+allOf:
+  - if:
+      not:
+        required:
+          - spi-slave
+    then:
+      properties:
+        "#address-cells":
+          const: 1
+    else:
+      properties:
+        "#address-cells":
+          const: 0
 
 patternProperties:
   "^slave$":