x86: Make the num_siblings CPU parameter per-CPU.

x86: Make the num_siblings CPU parameter per-CPU.

While it is unlikely that a system has a different number of siblings
for different physical CPUs,  make this parameter per-CPU for
consistency, and deal with the (so far theoretical) case that this is
different per CPU package.

Signed-off-by: Frank van der Linden <Frank.Vanderlinden@Sun.COM>