Reland "[NVPTX] Add folding for cvt.rn.bf16x2.f32" (#116417)

Reland https://github.com/llvm/llvm-project/pull/116109.

Fixes issue where operands were flipped. 

Per the PTX spec, a mov instruction packs the first operand as low, and
the second operand as high:
> ```
> // pack two 16-bit elements into .b32
> d = a.x | (a.y << 16)
> ```
On the other hand cvt.rn.f16x2.f32 instructions take high, than low
operands:
> For .f16x2 and .bf16x2 instruction type, two inputs a and b of .f32
type are converted into .f16 or .bf16 type and the converted values are
packed in the destination register d, such that the value converted from
input a is stored in the upper half of d and the value converted from
input b is stored in the lower half of d

0 files changed, 0 insertions, 0 deletions