Cache .ivy2 and .sbt within Chipyard root directory

[abejgonzalez]

Since .ivy2 and .sbt folders are small under normal Chipyard circumstances (<150MBs), go ahead and store them within the Chipyard root directory. This further isolates separate Chipyard repos from one another (this ivy2 sharing indirectly caused an issue where scala files would have no partial compilation). For those that want to override SBT_OPTS, they still can (as evidenced by the CI not changing - it still overrides the options). Additionally, this PR adds the SBT_OPTS on the command line so that the thin client can pick it up (fixes #1329). Finally, this resolves some minor build.sbt deprecation warnings.

Related PRs / Issues:
Fixes #1329

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you update the conda .conda-lock.yml file if you updated the conda requirements file?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?

[abejgonzalez]

@Mergifyio rebase

[mergify]

rebase

✅ Branch has been successfully rebased

[jerryz123]

If things can fail when the dirs don't exist, then we should just commit the directories with an empty file so the git clone will always produce it.