bhyve: Report SVM as disabled on AMD

[chuck]

Summary

bhyve with a Windows 2025 guest will hang/freeze with the message

rdmsr to register 0xc0010114

on a system with an AMD Ryzen 5. Evidently, recent versions of Windows
ignore the CPUID bits and still read this MSR.

Fix is to report Secure Virtual Machine (SVM) mode as disabled in the VM CR.

PR: 288308
Reported by: [e-mail]
Tested by: [e-mail]
Obtained from: Illumos