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 <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Alexandre Torgue <[e-mail]>

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

···
           - const: st,stm32h743
       - items:
           - enum:
+              - st,stm32h750i-art-pi
+          - const: st,stm32h750
+      - items:
+          - enum:
               - shiratech,stm32mp157a-iot-box # IoT Box
               - shiratech,stm32mp157a-stinger96 # Stinger96
               - st,stm32mp157c-ed1