sel4utils: s/CONFIG_IOMMU/CONFIG_ARM_SMMU

CONFIG_IOMMU does not exist on arm.

libsel4vspace/src/arch/arm/mapping.c

diff --git a/libsel4vspace/src/arch/arm/mapping.c b/libsel4vspace/src/arch/arm/mapping.c
index 285ef23..fe9b504 100644
--- a/libsel4vspace/src/arch/arm/mapping.c
+++ b/libsel4vspace/src/arch/arm/mapping.c
@@ -22,7 +22,7 @@
 
 int vspace_get_iospace_map_obj(UNUSED seL4_Word failed_bits, vspace_map_obj_t *obj)
 {
-    if (unlikely(obj == NULL) || !config_set(CONFIG_IOMMU)) {
+    if (unlikely(obj == NULL) || !config_set(CONFIG_ARM_SMMU)) {
         return EINVAL;
     }
 #ifdef CONFIG_ARM_SMMU