dt-bindings: stm32: document stm32mp135f-dk board

Add new entry for stm32mp135f-dk board.
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/stm32/stm32.yaml

@@ -55,6 +55,10 @@ properties:
           - enum:
               - st,stm32h750i-art-pi
           - const: st,stm32h750
+      - items:
+          - enum:
+              - st,stm32mp135f-dk
+          - const: st,stm32mp135
       - items:
           - enum:
               - shiratech,stm32mp157a-iot-box # IoT Box