[AMD] Add TritonAMDGPU dialect scaffolding (#4685)
This PR adds an TritonAMDGPU dialect to host future
AMD specific ops to help with AMD backend CodeGen.
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Co-authored-by: Ognjen Plavsic <ognjen.plavsic@luxoft.com>
Co-authored-by: Lei Zhang <antiagainst@gmail.com>