KVM SVM changes for 6.9:

 - Add support for systems that are configured with SEV and SEV-ES+ enabled,
   but have all ASIDs assigned to SEV-ES+ guests, which effectively makes SEV
   unusuable.  Cleanup ASID handling to make supporting this scenario less
   brittle/ugly.

 - Return -EINVAL instead of -EBUSY if userspace attempts to invoke
   KVM_SEV{,ES}_INIT on an SEV+ guest.  The operation is simply invalid, and
   not related to resource contention in any way.