KVM: selftests: Report per-vcpu demand paging rate from demand paging test

KVM: selftests: Report per-vcpu demand paging rate from demand paging test

Using the overall demand paging rate to measure performance can be
slightly misleading when vCPU accesses are not overlapped. Adding more
vCPUs will (usually) increase the overall demand paging rate even
if performance remains constant or even degrades on a per-vcpu basis. As
such, it makes sense to report both the total and per-vcpu paging rates.

Signed-off-by: Anish Moorthy <amoorthy@google.com>
Link: https://lore.kernel.org/r/20240215235405.368539-11-amoorthy@google.com
[sean: fix formatting]
Signed-off-by: Sean Christopherson <seanjc@google.com>