[llvm] [PowerPC] Add intrinsics and tests for basic Dense Math enablement instructions (PR #129913)

[Maryam Moghadas via llvm-commits]

https://github.com/maryammo commented:

Does it make sense to rename these instructions based on the latest RFC in this patch, since it adds the intrinsic for them, or should we do that in a separate patch, as it would require updating more places?

https://github.com/llvm/llvm-project/pull/129913