dt-bindings: arm: fsl: Add bindings for SolidRun i.MX8MP SoM and boards

Add bindings for SolidRun i.MX8M Plus System on Module based boards:

- CuBox-M is a complete produc with enclosure including the SoM
- HummingBoard Mate/Pro/Pulse/Ripple are evaluation boards with common
design but different available interfaces.

Signed-off-by: Josua Mayer <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

Documentation/devicetree/bindings/arm/fsl.yaml

···
           - const: polyhex,imx8mp-debix-som-a       # Polyhex Debix SOM A
           - const: fsl,imx8mp
 
+      - description: SolidRun i.MX8MP SoM based boards
+        items:
+          - enum:
+              - solidrun,imx8mp-cubox-m             # SolidRun i.MX8MP SoM on CuBox-M
+              - solidrun,imx8mp-hummingboard-mate   # SolidRun i.MX8MP SoM on HummingBoard Mate
+              - solidrun,imx8mp-hummingboard-pro    # SolidRun i.MX8MP SoM on HummingBoard Pro
+              - solidrun,imx8mp-hummingboard-pulse  # SolidRun i.MX8MP SoM on HummingBoard Pulse
+              - solidrun,imx8mp-hummingboard-ripple # SolidRun i.MX8MP SoM on HummingBoard Ripple
+          - const: solidrun,imx8mp-sr-som
+          - const: fsl,imx8mp
+
       - description: TechNexion EDM-G-IMX8M-PLUS SoM based boards
         items:
           - enum: