Function decide_caps 

fn decide_caps(
    req_fullcolor: bool,
    req_w: i32,
    req_h: i32,
    cap_yuv444: Option<i32>,
    cap_width_max: Option<i32>,
    cap_height_max: Option<i32>,
) -> CapsDecision

Resolve the requested chroma and geometry against the driver caps (None = unknown, ungated).