dt-bindings: clock: anlogic,dr1v90-cru: make external clocks optional

The main oscillator is the only required input clock for the CRU, while
the external CAN and WDT clocks are optional board-level inputs. The
binding currently requires all three clocks, forcing device trees for
boards without these external inputs to add stub fixed-clock nodes for
which no meaningful clock-frequency can be specified.

Allow the clocks and clock-names properties to contain just "osc",
optionally followed by either or both of "can_ext" and "wdt_ext".

Fixes: 155d900e4c ("dt-bindings: clock: add Anlogic DR1V90 CRU")
Signed-off-by: Junhui Liu <junhui.liu@pigmoral.tech>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Brian Masney <bmasney@redhat.com>

Documentation/devicetree/bindings/clock/anlogic,dr1v90-cru.yaml

@@ -17,15 +17,17 @@ properties:
     maxItems: 1
 
   clocks:
-    items:
-      - description: Main oscillator
-      - description: External CAN clock
-      - description: External WDT clock
+    minItems: 1
+    maxItems: 3
+    description:
+      The main oscillator is always required. Either or both of the external CAN
+      and WDT clocks may also be provided if the board routes them to the SoC.
 
   clock-names:
+    minItems: 1
     items:
       - const: osc
-      - const: can_ext
+      - enum: [can_ext, wdt_ext]
       - const: wdt_ext
 
   "#clock-cells":