drm/msm/hdmi: add "qcom,hdmi-tx-8998" compatible

Current driver already supports the msm8998 HDMI TX.
We just need to add the compatible string.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Marc Gonzalez <mgonzalez@freebox.fr>
Patchwork: https://patchwork.freedesktop.org/patch/605632/
Link: https://lore.kernel.org/r/20240724-hdmi-tx-v7-3-e44a20553464@freebox.fr


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>