dt-bindings: simple-framebuffer: allow standalone compatible

Qualcomm platforms use "simple-framebuffer" without a more specific
compatible. Allow that in the binding doc.

Signed-off-by: Luca Weiss <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Helge Deller <[e-mail]>

Documentation/devicetree/bindings/display/simple-framebuffer.yaml

···
 
 properties:
   compatible:
-    items:
-      - enum:
-          - apple,simple-framebuffer
-          - allwinner,simple-framebuffer
-          - amlogic,simple-framebuffer
+    oneOf:
+      - items:
+          - enum:
+              - apple,simple-framebuffer
+              - allwinner,simple-framebuffer
+              - amlogic,simple-framebuffer
+          - const: simple-framebuffer
       - const: simple-framebuffer
 
   reg: