use msr 0xc001100c to discover multi-node AMD processors

This is applicable only to the older processors that do not have the AMD
Topology extension.
Opteron 6100-series "Magny-Cours" processors had multiple nodes within a
package and didn't have the Topology extension. Without this change
FreeBSD would assume that those processors have a single L3 cache shared
by all cores while, in fact, each node has its own L3 cache.

Many thanks to Freddie Cash <fjwcash@gmail.com> for providing valuable
hardware information.

MFC after: 2 weeks