[llvm] [AArch64][GlobalISel] Select unmerging s128 FPR value into two s64 GPR values (PR #215995)

[Nathan Corbyn via llvm-commits]

https://github.com/cofibrant approved this pull request.

This makes sense to me--though I'm not very familiar with the semantics of `umov` so maybe shouldn't have the final say on this

https://github.com/llvm/llvm-project/pull/215995