i386: add bios linker/loader

This adds a dynamic bios linker/loader.
This will be used by acpi table generation
code to:
    - load each table in the appropriate memory segment
    - link tables to each other
    - fix up checksums after said linking

Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
