Add starfive-visionfive-v2 as example rv64 board

[prashanthswami]

We should ideally have at least one RISC-V board in our test group to limit future regression. Further work will have to be done to actually enable a toolchain that can build this test. The Starfive VisionFive V2 board was chosen here as an open-source board that has been referenced in the public issues.

Confirmed success of this mocked device test on a RISC-V QEMU instance.

[prashanthswami]

For review: @malfet CC: @GlassOfWhiskey - the riscv_hwprobe mock stuff should merge cleanly with your current PR, but the hwcap mock may conflict slightly. Need to also see if I should guard it with Linux 6.4 based on the discussion thread there.