drm/mediatek: mtk_dpi: Move the input_2p_en bit to platform data

drm/mediatek: mtk_dpi: Move the input_2p_en bit to platform data

In preparation for adding support for MT8195's HDMI reserved DPI
instance, move the input_2p_en bit for DP_INTF to platform data.

While at it, remove the input_2pixel member from platform data as
having this bit implies that the 2pixel feature must be enabled.

Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250217154836.108895-7-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>