powerpc/pseries: Add a helper for form1 cpu distance

[ Upstream commit ef31cb83

 ]

This helper is only used with the dispatch trace log collection.
A later patch will add Form2 affinity support and this change helps
in keeping that simpler. Also add a comment explaining we don't expect
the code to be called with FORM0

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210812132223.225214-5-aneesh.kumar@linux.ibm.com
Stable-dep-of: b277fc79

 ("powerpc/papr_scm: Update the NUMA distance table for the target node")
Signed-off-by: Sasha Levin <sashal@kernel.org>