re-enable AMD Topology extension on certain models if disabled by BIOS

re-enable AMD Topology extension on certain models if disabled by BIOS

Some BIOSes disable AMD Topology extension on AMD Family 15h notebook
processors.  We re-enable the extension, so that we can properly discover
core and cache topology.  Linux seems to do the same.

Reported by:	Johannes Dieterich <dieterich.joh@gmail.com>
Reviewed by:	jhb, kib
Tested by:	Johannes Dieterich <dieterich.joh@gmail.com>
		(earlier version)
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D5883