acpi: build_amd_iommu: use acpi_table_begin()/acpi_table_end() instead of build_header()

it replaces error-prone pointer arithmetic for build_header() API,
with 2 calls to start and finish table creation,
which hides offsets magic from API user.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20210924122802.1455362-21-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/acpi-build.c

@@ -2341,12 +2341,12 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker, const char *oem_id,
                 const char *oem_table_id)
 {
     int ivhd_table_len = 24;
-    int iommu_start = table_data->len;
     AMDVIState *s = AMD_IOMMU_DEVICE(x86_iommu_get_default());
     GArray *ivhd_blob = g_array_new(false, true, 1);
+    AcpiTable table = { .sig = "IVRS", .rev = 1, .oem_id = oem_id,
+                        .oem_table_id = oem_table_id };
 
-    /* IVRS header */
-    acpi_data_push(table_data, sizeof(AcpiTableHeader));
+    acpi_table_begin(&table, table_data);
     /* IVinfo - IO virtualization information common to all
      * IOMMU units in a system
      */
@@ -2431,10 +2431,7 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker, const char *oem_id,
                                  0x48,                      /* special device */
                                  8);
     }
-
-    build_header(linker, table_data, (void *)(table_data->data + iommu_start),
-                 "IVRS", table_data->len - iommu_start, 1, oem_id,
-                 oem_table_id);
+    acpi_table_end(linker, &table);
 }
 
 typedef