[AMDGPU] Instruction Type Pipeline

[AMDGPU] Instruction Type Pipeline

This patch implements a DAG mutation which adds edges between different groups of instructions. The purpose is to try to generate code that conforms to a pipeline (groupA instructions occur before groupB, groupB -> groupC, and so on). Currently the pipeline order is hardcoded as VMEM->DSRead->MFMA->DSWrite, but the patch was designed to be easily extensible. Alias analysis is problematic for pipelining as memory instructions will usually not be able to be reordered w.r.t one another.

Differential Revision: https://reviews.llvm.org/D125997