dt-bindings: yamllint: Enable quoted string check

yamllint has a quoted string check. Enable the check aligned with the DT schema style which is only using quotes when necessary with the exception of regex patterns. There's also the frequent occurrence of '/' which we allow rather than fixing.

---
 Documentation/devicetree/bindings/.yamllint | 5 +++++
 1 file changed, 5 insertions(+)

index 4abe9f0a1d46..fea5231e1320 100644
@@ -1,6 +1,11 @@
 extends: relaxed
 
 rules:
+  quoted-strings:
+    required: only-when-needed
+    extra-allowed:
+      - '[$^,[]'
+      - '^/$'
   line-length:
     # 80 chars should be enough, but don't fail if a line is longer
     max: 110

2.39.2