[llvm] [Lanai] Use `softPromoteHalfType` (PR #175137)

[Trevor Gross via llvm-commits]

tgross35 wrote:

I was planning to follow up with that, but figured that it is worth swapping the remaining targets first since some need more specific updates, and in case of problems changing the default.

Would you prefer me to drop this patchset and just do that? If it's fine to apply these first, I'll mark this one through https://github.com/llvm/llvm-project/pull/175141 ready to review (still need to figure something out with xcore)

https://github.com/llvm/llvm-project/pull/175137