Don't advertise the "OS visible workarounds" feature in cpuid.80000001H:ECX.
bhyve doesn't emulate the MSRs needed to support this feature at this time.

Don't expose any model-specific RAS and performance monitoring features in
cpuid leaf 80000007H.

Emulate a few more MSRs for AMD: TSEG base address, TSEG address mask and
BIOS signature and P-state related MSRs.

This eliminates all the unimplemented MSRs accessed by Linux/x86_64 kernels
2.6.32, 3.10.0 and 3.17.0.