iris: Disable CCS_E for 32-bit floating point textures.
A while back, Michael Larabel noticed that Paraview's Wavelet Volume case runs significantly slower on iris than i965. It turns out this is because we enable CCS_E for 32-bit floating point formats, while i965 disables it, with an oblique comment saying that we benchmarked it (on what exactly?) and determined that it was a loss. Paraview uses both R32_FLOAT and R32G32B32A32_FLOAT, and I observed large framerate drops when enabling CCS_E for either format. However, several other benchmarks (Aztec Ruins, many Synmark cases) use 16-bit floating point formats, with no apparent ill effects. So, disable compression for 32-bit float formats for now, but leave it enabled for 16-bit float formats as they seem to be working fine. Improves performance in Paraview's Wavelet Volume test by 62% on a Skylake GT4e. Fixes: 3cfc6a20 ("iris: Fill out res->aux.possible_usages")
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