acpi: Support generating a multi-function _DSM for devices

Add a function to generate ACPI code for a _DSM method for a device.
This includes functions for starting and ending each part of the _DSM.

Signed-off-by: Simon Glass <sjg@chromium.org>
[bmeng: fix the "new blank line at EOF" git warning]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
5 files changed