KVM: set_memory_region: Refactor prepare_memory_region()

This patch drops the parameter old, a copy of the old memory slot, and
adds a new parameter named change to know the change being requested.

This not only cleans up the code but also removes extra copying of the
memory slot structure.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

virt/kvm/kvm_main.c

@@ -856,7 +856,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		slots = old_memslots;
 	}
 
-	r = kvm_arch_prepare_memory_region(kvm, &new, old, mem);
+	r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
 	if (r)
 		goto out_slots;