[AMDGPU] Adopt new lowering sequence for `fdiv16` (#109295)

The current lowering of `fdiv16` can generate incorrectly rounded result
in some cases. The new sequence was provided by the HW team, as shown
below written in C++.


```
half fdiv(half a, half b) {
  float a32 = float(a);
  float b32 = float(b);
  float r32 = 1.0f / b32;
  float q32 = a32 * r32;
  float e32 = -b32 * q32 + a32;
  q32 = e32 * r32 + q32;
  e32 = -b32 * q32 + a32;
  float tmp = e32 * r32;
  uin32_t tmp32 = std::bit_cast<uint32_t>(tmp);
  tmp32 = tmp32 & 0xff800000;
  tmp = std::bit_cast<float>(tmp32);
  q32 = tmp + q32;
  half q16 = half(q32);
  q16 = div_fixup_f16(q16);
  return q16;
}
```

Fixes SWDEV-477608.

0 files changed, 0 insertions, 0 deletions