kernel - Do not try to apply certain hw errata fixes if in a VM guest

* Do not try to apply certain hw errata fixes (721) if in a VM guest.

Submitted-by: vsrinivas

Conflicts:
	sys/cpu/x86_64/include/specialreg.h
kernel -- vmm: SVM support: complete VMCB definition, guest entry loop.

Can VMRUN, but #VMEXITs on Invalid Guest state, as expected.