drm/mediatek: dpi: Add dp_intf support

Dpintf is the displayport interface hardware unit. This unit is similar
to dpi and can reuse most of the code.

This patch adds support for mt8195-dpintf to this dpi driver. Main
differences are:
 - 4 pixels for one iteration for dp_intf while dpi is 1 pixel for one
   iteration.
 - Input of dp_intf is two pixels per iteration.
 - Some register contents differ slightly between the two components.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20220705102530.1344-6-rex-bc.chen@mediatek.com/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>