Parallelize UVM tests without LSF (in CI)

RISC-V DV gives us the option to specify a job submission command to parallelize simulation jobs. We do not have a full LSF setup, and I don't really want to build one for CI.

I see two options:

• Find a small tool which we can use as job submission command, similar to bsub -Is (which is what the RISCV-DV documentation suggests).
• Parallelize on the dv/uvm/core_ibex/Makefile level
• Manually split up the tests and run them in parallel through Azure Pipelines jobs, i.e. run make TEST=test_1, make TEST=test_2, etc. in parallel.

I think I'd prefer Option 1. I did have a quick look at GNU parallel and I'm not sure it's up to the job, but I'm quite sure there must be something out there.

Start with dv/uvm/core_ibex/Makefile and the RISC-V DV documentation describing the bsub-style job submission command. Compare the three proposed approaches, then verify that the UVM tests run in parallel in CI without requiring LSF and that the chosen approach is reflected in the Azure Pipelines jobs.