nvk: Use suld.constant for EDB uniform texel buffers
In 2183bc73 ("nvk: Use suld for EDB uniform texel buffers"), we started using suld instead of tld for EDB uniform texel buffers because we needed it for correctness. However, it's slow as mud. Using suld.constant seems to fix the performance regression. I don't know if it's quite tld performance, but it's close.