vspace: update for 40-bit-PA + hyp

exclude references to PUD methods that do not exist in this
configuration.
diff --git a/libsel4vspace/src/sel4_arch/aarch64/mapping.c b/libsel4vspace/src/sel4_arch/aarch64/mapping.c
index b980d0c..49bf5eb 100644
--- a/libsel4vspace/src/sel4_arch/aarch64/mapping.c
+++ b/libsel4vspace/src/sel4_arch/aarch64/mapping.c
@@ -28,11 +28,13 @@
         obj->type = seL4_ARM_PageDirectoryObject;
         obj->map_fn = seL4_ARM_PageDirectory_Map;
         return 0;
+#if !(defined CONFIG_ARM_HYPERVISOR_SUPPORT && defined CONFIG_ARM_PA_SIZE_BITS_40)
     case SEL4_MAPPING_LOOKUP_NO_PUD:
         obj->size_bits = seL4_PUDBits;
         obj->type = seL4_ARM_PageUpperDirectoryObject;
         obj->map_fn = seL4_ARM_PageUpperDirectory_Map;
         return 0;
+#endif
     default:
         return EINVAL;
     }