ACPI: add documentation about ACPI 5 enumeration

Add a document that describes how to take advantage of ACPI enumeration for
buses like platform, I2C and SPI. In addition to that we document how to
translate ACPI GpioIo and GpioInt resources to be useful in Linux device
drivers.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>