[llvm] AMDGPU/GlobalISel: Legalize BF16 FSQRT, FLOG2, and FEXP2 (PR #214123)

[Petar Avramovic via llvm-commits]

https://github.com/petar-avramovic commented:

should add some ll test, or run line in some of existing sdag tests

https://github.com/llvm/llvm-project/pull/214123