[ROCm][CK][Inductor] enable gfx950 for max autotune with CK (pytorch#159195)

+ update inductor config for new gfx arch
+ fixes in codegen for conv2d and ck-tile matmul
+ use appropriate fp8 dtypes
+ test cleanup

Pull Request resolved: pytorch#159195
Approved by: https://github.com/chenyang78

Author: tenpercent