vmm: Correctly suspend and resume the vmm driver.

Previously, VMXON would be executed on a resume, contrary to proper
initalization. The contents of MSR_IA32_FEATURE_CONTROL may be lost on
suspension, therefore must be restored. Likewise, the VMX Enable bit may be
cleared upon suspend, requiring it to be re-set.

Concretely disable VMX on suspend, and re-enable it on resume.

Note: any IOMMU context will remain lost for any enabled vmm devices.

Signed-off-by: Joshua Rogers <Joshua@Joshua.Hu>
Reviewed by: jhb,imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1419