dt-bindings: arm: Add DH electronics i.MX8M Plus DHCOM and PDK2

Add DT compatible string for DH electronics i.MX8M Plus DHCOM and PDK2
into YAML DT binding document. This system is a general purpose SoM and
evaluation board.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: devicetree@vger.kernel.org
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/fsl.yaml

@@ -920,6 +920,8 @@ properties:
       - description: i.MX8MP based Boards
         items:
           - enum:
+              - dh,imx8mp-dhcom-som       # i.MX8MP DHCOM SoM
+              - dh,imx8mp-dhcom-pdk2      # i.MX8MP DHCOM SoM on PDK2 board
               - fsl,imx8mp-evk            # i.MX8MP EVK Board
               - gateworks,imx8mp-gw74xx   # i.MX8MP Gateworks Board
               - toradex,verdin-imx8mp     # Verdin iMX8M Plus Modules