acpi: Add support for SSDT generation

Some devices need to generate code for the Secondary System Descriptor
Table (SSDT). Add a method to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
4 files changed