vmm(4): Enable support for AMD-V (SVM) CPUs.

vmm(4): Enable support for AMD-V (SVM) CPUs.

Tested on the following CPUs:

AMD C-60 APU
AMD GX-412TC SOC (PCEngines APU2C4)
AMD Opteron(tm) Processor 6128

... and various others via bochs/simulators, on a variety of different
guest VM types. Also verified no regressions on my x230 Intel machine
since this diff slightly changes CPUID behaviour WRT cache information.

ok deraadt@