[DT] Add support for emulating GPU data-tiling on CPU.

[hanhanW]

The revision sets up a path to generate GPU layouts on CPU backends. The revision uses --iree-gpu-test-target flag to control the target GPU.

Note: both --iree-codegen-cpu-experimental-emulate-gpu-data-tiling and --iree-gpu-test-target flags are required for the emulation.

It is a step towards https://gist.github.com/bjacob/137e848512d83adcc02e995d816831ec

NOTE: This will be merged into the shared/gpu-data-tiling-materialize-encoding branch. We will land it to main with better code structure. The revision adds unnecessary deps betwee Common/CPU and Common/GPU. It is fine IMO, because it needs to be fixed before moving them to main branch.