iommu: fix arm build after e9be34be5

The function iommu_share_p2m_table is used by both ARM and x86 but
hap_enabled macro is x86 only. Put the ASSERT under CONFIG_X86.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/passthrough/iommu.c

@@ -505,7 +505,9 @@ int iommu_do_domctl(
 
 void iommu_share_p2m_table(struct domain* d)
 {
+#ifdef CONFIG_X86
     ASSERT(hap_enabled(d));
+#endif
     /*
      * iommu_use_hap_pt(d) cannot be used here because during domain
      * construction need_iommu(d) will always return false here.