dt-bindings: display: mediatek: control dpi pins mode to avoid leakage

[ Upstream commit b0ff9b590733079f7f9453e5976a9dd2630949e3 ]

Add property "pinctrl-names" to swap pin mode between gpio and dpi mode.
Set the dpi pins to gpio mode and output-low to avoid leakage current
when dpi disabled.

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