renderer: use nominal max luminance for peak detection check
Static HDR10 metadata may lie about the actual luminance range of the source. To be more conservative, use only the true max peak luminance for this check. This will still disable peak detection if outputting to full range PQ, or if using tuned HLG, but will enable peak detection otherwise (for standard HDR content) - even if HDR10 metadata claims it would not be needed.