dt-bindings: can: fsl,flexcan: add common 'can-transceiver' for fsl,flexcan

Add common 'can-transceiver' children node for fsl,flexcan.

Fix below warning:
arch/arm64/boot/dts/freescale/fsl-ls1028a-rdb.dtb: can@2180000: 'can-transceiver' does not match any of the regexes: 'pinctrl-[0-9]+'
        from schema $id: http://devicetree.org/schemas/net/can/fsl,flexcan.yaml#

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/all/20240629021754.3583641-1-Frank.Li@nxp.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/fsl,flexcan.yaml

@@ -80,6 +80,10 @@ properties:
       node then controller is assumed to be little endian. If this property is
       present then controller is assumed to be big endian.
 
+  can-transceiver:
+    $ref: can-transceiver.yaml#
+    unevaluatedProperties: false
+
   fsl,stop-mode:
     description: |
       Register bits of stop mode control.