[llvm] AMDGPU: Add some leaf intrinsics to isAlwaysUniform (PR #101925)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I think uniformity analysis will always tell it is uniform because it has no divergent arguments. Do you think searching this table is faster?

The table is only used once to initialize special overriding map entries. The point of this is we can use it for trivial checks without using full uniformity analysis 

https://github.com/llvm/llvm-project/pull/101925