Documentation: ACPI: Align the SSDT overlays file with the code

This updates the following:

1) The ASL code to follow latest ACPI requirements, i.e.
   - static buffer to be defined outside of the method
   - The _ADR and _HID shouldn't be together for the same device

2) EFI section relies on the additional kernel configuration option,
   i.e. CONFIG_EFI_CUSTOM_SSDT_OVERLAYS

3) Refer to ACPI machine language as AML (capitalized)

4) Miscellaneous amendments

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>