Support FV on aws-lc FIPS branches

[bryce-shang]

There will be several FIPS branches(normally prefixed with fips-, e.g. fips-2021-10-20) in aws-lc repo. The support will need to address the build(FIPS vs non-FIPS build) and source code(FIPS branch does not have latest code) differences, which mean the support may need to be branch-specific. Today, aws-lc CI loads branch-specific build-spec yml files.