Detach the firesim/chipyard build.sbts

[jerryz123]

Now firesim uses its own build.sbt to compile the goldengate/midas/firesim-main jar, while the target jar is compiled using chipyard's build.sbt. This lets us move towards detaching these projects.

The new chipyard-symlink symlink is necessary because the sim/build.sbt expects all the the chipyard-managed sources in firesim-as-library mode to be below it in the file tree.

Related PRs / Issues

UI / API Impact

Verilog / AGFI Compatibility

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[joonho3020]

LGTM