Fix topology enumeration issues exposed by AMD Bulldozer Family 15h processor.

Initialize CPUID.80000008H:ECX[7:0] with the number of logical processors in
the package. This fixes a panic during early boot in NetBSD 7.0 BETA.

Clear the Topology Extension feature bit from CPUID.80000001H:ECX since we
don't emulate leaves 0x8000001D and 0x8000001E. This fixes a divide by zero
panic in early boot in Centos 6.4.

Tested on an "AMD Opteron 6320" courtesy of Ben Perrault.

Reviewed by: grehan