add description for postmask
postmask is used control round corner for display frame
Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
        "mediatek,<chip>-disp-aal"              - adaptive ambient light controller
        "mediatek,<chip>-disp-gamma"            - gamma correction
        "mediatek,<chip>-disp-merge"            - merge streams from two RDMA sources
+       "mediatek,<chip>-disp-postmask"         - control round corner for display frame
        "mediatek,<chip>-disp-split"            - split stream to two encoders
        "mediatek,<chip>-disp-ufoe"             - data compression engine
        "mediatek,<chip>-dsi"                   - DSI controller, see mediatek,dsi.txt