Do not apply errata 721 workaround when under hypervisor, since typical hypervisor does not implement access to the required MSR, causing #GP on boot.
Do not apply errata 721 workaround when under hypervisor, since
typical hypervisor does not implement access to the required MSR,
causing #GP on boot.

Reported and tested by:	olgeni
PR:	amd64/170388
MFC after:	3 days

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