powerpc/pseries: Add wait interval counter definitions to struct lppaca

The hypervisor exposes accumulated partition scheduling interval times
in the VPA (lppaca). These can be used to implement a simple stolen time
in the guest without complex and costly dtl scanning.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Link: https://lore.kernel.org/r/20220902085316.2071519-2-npiggin@gmail.com