tests: add smbios testing

Add tests to find and verify the smbios entry point structure,
and to walk and perform checks on the actual smbios tables.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
