spapr: set vsmt to MAX(8, smp_threads)

spapr: set vsmt to MAX(8, smp_threads)

We ignore silently the value of smp_threads when we set
the default VSMT value, and if smp_threads is greater than VSMT
kernel is going into trouble later.

Fixes: 8904e5a750
("spapr: Adjust default VSMT value for better migration compatibility")

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
(cherry picked from commit 4ad64cbd0c3f9df15be5f7d1c920285551e802ca)
Signed-off-by: Greg Kurz <groug@kaod.org>