x86: acpi: Resume OS if resume vector is found

In an S3 resume path, U-Boot does everything like a cold boot except
in the last_stage_init() it jumps to the OS resume vector.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Stefan Roese <sr@denx.de>