dt-bindings: arm: stm32: Add compatible strings for Protonic T1L boards

This boards are based on STM32MP151AAD3 and use 10BaseT1L for
communication.

- PRTT1C - 10BaseT1L switch
- PRTT1S - 10BaseT1L CO2 sensor board
- PRTT1A - 10BaseT1L multi functional controller

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

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

@@ -51,6 +51,14 @@ properties:
               - st,stm32mp135f-dk
           - const: st,stm32mp135
 
+      - description: ST STM32MP151 based Boards
+        items:
+          - enum:
+              - prt,prtt1a   # Protonic PRTT1A
+              - prt,prtt1c   # Protonic PRTT1C
+              - prt,prtt1s   # Protonic PRTT1S
+          - const: st,stm32mp151
+
       - description: DH STM32MP153 SoM based Boards
         items:
           - const: dh,stm32mp153c-dhcom-drc02