[clang] [llvm] [mlir] [AMDGPU] Generalize global.load.lds to buffer fat pointers (PR #134911)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> * Per your comments on the previous PR, a new intrinsic for p7 is also out - or were you just objecting to the naming?

Mostly this, but I also dont' really understand why this doesn't fit into the existing raw_buffer_load_lds 

https://github.com/llvm/llvm-project/pull/134911