dt-bindings: arm: stm32: Add compatible strings for ART-PI board

Art-pi based on stm32h750xbh6, with following resources:

-8MiB QSPI flash
-16MiB SPI flash
-32MiB SDRAM
-AP6212 wifi, bt, fm

detail information can be found at:
https://art-pi.gitee.io/website/Signed-off-by: dillon min <dillon.minfei@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

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

@@ -51,6 +51,10 @@ properties:
               - st,stm32h743i-disco
               - st,stm32h743i-eval
           - const: st,stm32h743
+      - items:
+          - enum:
+              - st,stm32h750i-art-pi
+          - const: st,stm32h750
       - items:
           - enum:
               - shiratech,stm32mp157a-iot-box # IoT Box