x86: Move acpi_s3.h to include/acpi/

This header relates to ACPI and we are about to add some more ACPI
headers. Move this one into a new directory so they are together.

The header inclusion in pci_rom.c is not specific to x86 anymore, so drop
the #ifdef CONFIG_X86.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>