[clang] [llvm] [AMDGPU][WIP] Add support for i64/f64 readlane, writelane and readfirstlane operations. (PR #89217)

[Vikram Hegde via llvm-commits]

vikramRH wrote:

1. Review comments
2. improve GIsel lowering
3. add tests for half, bfloat, float2, ptr, vector of ptr and int
4. removed gfx700 checks from writelane test since it caused issues with f16 legalization. is this required ?

https://github.com/llvm/llvm-project/pull/89217