More tests in nightly regression

[davidharrishmc]

Performance validation: CoreMark, Embench, cache, branch, ways to detect issues
Tests with multiple simulators
Lockstep tests
Code coverage
Functional coverage

Some of this depends on having a single test bench that supports lockstep, and replacing run-elf / run-elf-cov, iter-elf.

Update testplan.md when done

[davidharrishmc]

VCS added to nightly regression. Verilator too.

[davidharrishmc]

Added lockstep tests of coverage and wally-riscv-arch-test privilege with iterelf PR #866
Added lockstep test of buildroot boot

[jordancarlin]

Might be time to start thinking about adding functional coverage from cvw-arch-verif to nightly regression

[jordancarlin]

Also add riscv-arch-test priv tests in lockstep to nightly. This should include privileged, pmp*, and vm_sv*.

[jordancarlin]

Coremark, embench, and cache validation added to nightly.

Looks like the only things left from this issue are branch prediction and maybe checking code/functional coverage in nightly.