x86: acpi: Turn on ACPI mode for S3

Before jumping to OS waking up vector, we need turn on ACPI mode
for S3, just like what we do for a normal boot.

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