spapr_numa: create a vcpu associativity helper

spapr_numa: create a vcpu associativity helper

The work to be done in h_home_node_associativity() intersects
with what is already done in spapr_numa_fixup_cpu_dt(). This
patch creates a new helper, spapr_numa_get_vcpu_assoc(), to
be used for both spapr_numa_fixup_cpu_dt() and
h_home_node_associativity().

While we're at it, use memcpy() instead of loop assignment
to created the returned array.

Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20200904172422.617460-3-danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>