acpi: convert linker from GArray to BIOSLinker structure

Patch just changes type of of linker variables to
a structure, there aren't any functional changes.

Converting linker to a structure will allow to extend
it functionality in follow up patch adding sanity blob
checks.

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