[llvm] [AArch64] Remove redundant fmovs when bitcasting from ext/trunc of bitcast (PR #175983)

[Amina Chabane via llvm-commits]

https://github.com/Amichaxx approved this pull request.

Thank you Kerry, LGTM.

It seems LLVM/GCC generate some funny looking assembly for this [case](https://godbolt.org/z/5nGMnc3ch):
```
define dso_local noundef float @extend_half(_Float16)(half noundef %x) local_unnamed_addr {
entry:
  %0 = bitcast half %x to i16
  %conv = zext i16 %0 to i32
  %1 = bitcast i32 %conv to float
  ret float %1
}
```
I believe this can become `fmov h0, h0`.

https://github.com/llvm/llvm-project/pull/175983