[llvm] AMDGPU: Use pattern to select instruction for intrinsic llvm.fptrunc.round (PR #105761)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

I don't like secret opcodes that are not vendor opcodes. If it is a standard named opcodes, I prefer to advertise your achievemnts.

https://github.com/llvm/llvm-project/pull/105761