dt-bindings: display: mediatek: update dpi supported chips

Add descriptions about supported chips, including MT2701 & MT8173 &
mt8183

Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: CK Hu <ck.hu@mediatek.com>