acpi: Don't reset the tables with every new generation

At present if SSDT and DSDT code is created, only the latter is retained
for examination by the 'acpi items' command. Fix this by only resetting
the list when explicitly requested.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/x86/lib/acpi_table.c

@@ -531,6 +531,7 @@ ulong write_acpi_tables(ulong start_addr)
 
 	debug("ACPI: Writing ACPI tables at %lx\n", start_addr);
 
+	acpi_reset_items();
 	acpi_setup_base_tables(ctx, start);
 
 	debug("ACPI:    * FACS\n");