KVM: selftests: arm64: Rename helper in set_id_regs to imply VM scope

Prepare for a later change that'll cram in per-vCPU feature ID test
cases by renaming the current test case.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240502233529.1958459-5-oliver.upton@linux.dev


Signed-off-by: Marc Zyngier <maz@kernel.org>