KVM: PPC: Book3S HV: Implement scheduling wait interval counters in the VPA

PAPR specifies accumulated virtual processor wait intervals that relate
to partition scheduling interval times. Implement these counters in the
same way as they are repoted by dtl.

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220908132545.4085849-5-npiggin@gmail.com