x86: Prevent from missing the FADT chaining

Recent approach with FADT writer shows that there is
a room for subtle errors. Prevent this from happening
again by introducing acpi_add_fadt() helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/tangier/acpi.c b/arch/x86/cpu/tangier/acpi.c
index ffaa56a..1c667c7 100644
--- a/arch/x86/cpu/tangier/acpi.c
+++ b/arch/x86/cpu/tangier/acpi.c
@@ -52,11 +52,7 @@
 
 	header->checksum = table_compute_checksum(fadt, header->length);
 
-	acpi_add_table(ctx, fadt);
-
-	acpi_inc(ctx, sizeof(struct acpi_fadt));
-
-	return 0;
+	return acpi_add_fadt(ctx, fadt);
 }
 ACPI_WRITER(5fadt, "FADT", tangier_write_fadt, 0);