drm/mediatek: Add lut diff flag for new gamma hardware support

mt8183 gamma module usage is different with before soc,
gamma odd(index start from 0) lut value set to hardware
register should be
the difference of current lut value with last lut value.

for example, chrome os user space set lut
like this(only r chanel for example):
2 4 6 8 10 12.
1) mt8183 gamma driver should set the gamma lut to hardware
register like this:
2 [2] 6 [2] 10 [2]
the value with [] is the difference value
2)gamma hardware process display data with original lut

Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20220428085829.15855-2-yongqiang.niu@mediatek.com/


Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.com>
Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.corp-partner.google.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>