acpi: introduce TYPE_ACPI_DEVICE_IF interface

acpi: introduce TYPE_ACPI_DEVICE_IF interface

... it will be used to abstract generic ACPI bits from
device that implements ACPI interface.

ACPIOSTInfo type is used for passing-through raw _OST
event/status codes reported by guest OS to a management
layer. It lets management tools interpret values
as specified by ACPI spec if it is interested in it.

QEMU doesn't encode these values as enum, since it
doesn't need to handle them and it allows interface
to scale well without any changes in QEMU while guest
OS and management evolves in time.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>