Provide a constructor that takes the base address in addition to the
PC-specific one.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1372254743-15808-12-git-send-email-armbru@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>