dt-bindings: display: imx: add HDMI PAI for i.MX8MP

dt-bindings: display: imx: add HDMI PAI for i.MX8MP

Add binding for the i.MX8MP HDMI parallel Audio interface block.

The HDMI TX Parallel Audio Interface (HTX_PAI) is a digital module that
acts as the bridge between the Audio Subsystem to the HDMI TX Controller.
This IP block is found in the HDMI subsystem of the i.MX8MP SoC.

Aud2htx module in Audio Subsystem, HDMI PAI module and HDMI TX
Controller compose the HDMI audio pipeline.

In fsl,imx8mp-hdmi-tx.yaml, add port@2 that is linked to pai_to_hdmi_tx.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Link: https://lore.kernel.org/r/20250923053001.2678596-2-shengjiu.wang@nxp.com