[llvm] [AMDGPU][GlobalISel] Implement missing rules for G_TRUNC legalization (PR #180647)

[Petar Avramovic via llvm-commits]

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

Need to test G_TRUNC, check inline comment on how to generate some

https://github.com/llvm/llvm-project/pull/180647