KVM: set_memory_region: Refactor commit_memory_region()

This patch makes the parameter old a const pointer to the old memory
slot and adds a new parameter named change to know the change being
requested: the former is for removing extra copying and the latter is
for cleaning up the code.

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

arch/s390/kvm/kvm-s390.c

@@ -1001,7 +1001,8 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 
 void kvm_arch_commit_memory_region(struct kvm *kvm,
 				struct kvm_userspace_memory_region *mem,
-				struct kvm_memory_slot old)
+				const struct kvm_memory_slot *old,
+				enum kvm_mr_change change)
 {
 	int rc;