powerpc/pseries: new lparcfg key/value pair: partition_affinity_score

The H_GetPerformanceCounterInfo (GPCI) PHYP hypercall has a subcall,
Affinity_Domain_Info_By_Partition, which returns, among other things,
a "partition affinity score" for a given LPAR.  This score, a value on
[0-100], represents the processor-memory affinity for the LPAR in
question.  A score of 0 indicates the worst possible affinity while a
score of 100 indicates perfect affinity.  The score can be used to
reason about performance.

This patch adds the score for the local LPAR to the lparcfg procfile
under a new 'partition_affinity_score' key.

Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Acked-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200727184605.2945095-2-cheloha@linux.ibm.com