[Tracking Issue] Unified Device, Target and Memory Scope Planning

[mbs-octoml]

This issue is to track progress for unified-device-target-and-memory-scope-planning

See apache/tvm-rfcs#38.

cc @Hzfengsy @junrushao

[mbs-octoml]

The RFC is moribund at the moment while we clear off some more pressing issues. I'd like to pick this up again in 2022Q1 with more detail in the RFC after discussions with @Mousius who's tackling the companion Target vs 'codegen compiler name' disconnect.

I see this as enabling more uniform support for mixing and matching between library implementations, external codegen, and the built-in TIR codegen.