drm/mediatek: Fix YCbCr422 color format issue for DP

Setting up misc0 for Pixel Encoding Format.

According to the definition of YCbCr in spec 1.2a Table 2-96,
0x1 << 1 should be written to the register.

Use switch case to distinguish RGB, YCbCr422,
and unsupported color formats.

Fixes: f70ac097 ("drm/mediatek: Add MT8195 Embedded DisplayPort driver")
Signed-off-by: Liankun Yang <liankun.yang@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241025083036.8829-2-liankun.yang@mediatek.com/


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