freedreno/a6xx: Name texture descriptor bit
This appears to do the same thing as CLAMPENABLE on a3xx. That is, it clamps the result to [0, 1] for unorm formats and [-1, 1] for snorm formats *after* filtering. In particular it's now more easily observable with cubic filtering, because cubic filtering can produce values outside the original range. Presumably this only matters with linear filtering due to rounding errors when computing the weighted average.