dt-bindings: mediatek,dpi: add mt8192 to mediatek,dpi

Add compatible "mediatek,mt8192-dpi" for the mt8192 dpi.

Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>