kvm: fix compilation on s390

s390 does not have memremap, even though in this particular case it
would be useful.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -1761,8 +1761,10 @@ static int __kvm_map_gfn(struct kvm_memory_slot *slot, gfn_t gfn,
 	if (pfn_valid(pfn)) {
 		page = pfn_to_page(pfn);
 		hva = kmap(page);
+#ifdef CONFIG_HAS_IOMEM
 	} else {
 		hva = memremap(pfn_to_hpa(pfn), PAGE_SIZE, MEMREMAP_WB);
+#endif
 	}
 
 	if (!hva)