* Fix fmha fwd precision issue on MI3XX series
For fmha fwd fp16 cases, we found that using
impl::cast_tile_pk_fp16_fp32 for casting P would lead to precision
issues, since it uses __builtin_amdgcn_cvt_pkrtz, which is round to zero.
For examaple, fixing K,V to be all 1, and Q is random, which outputs are
expected to be all 1. But we found that it would have some incorrect
outputs 0.9995, which are smaller than the atol 0.001. (1 - 0.9995 =
0.0005 < 0.001) Thus, ck do not report this error.
* Add option to switch rtn/rtz for fmha fwd
9fcf21a4ec