KVM: SVM: Implement Caretaker SVM VMCB lifecycle and exit dispatch

Implement AMD SVM Caretaker VMCB preservation, exit decoding, and detach-time serialization in arch/x86/kvm/svm/caretaker.c. Signed-off-by: Pasha Tatashin pasha.tatashin@soleen.com — arch/x86/kv