x86/CPUID: suppress IOMMU related hypervisor leaf data

Now that the IOMMU for guests can't be enabled "on demand" anymore,
there's also no reason to expose the related CPUID bit "just in case".

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/traps.c

@@ -1050,7 +1050,8 @@ void cpuid_hypervisor_leaves(const struct vcpu *v, uint32_t leaf,
          * Indicate that memory mapped from other domains (either grants or
          * foreign pages) has valid IOMMU entries.
          */
-        res->a |= XEN_HVM_CPUID_IOMMU_MAPPINGS;
+        if ( is_iommu_enabled(d) )
+            res->a |= XEN_HVM_CPUID_IOMMU_MAPPINGS;
 
         /* Indicate presence of vcpu id and set it in ebx */
         res->a |= XEN_HVM_CPUID_VCPU_ID_PRESENT;