libata: Signal that our SATL supports WRITE SAME(16) with UNMAP

Until now identifying that a device supports WRITE SAME(16) with the
UNMAP bit set has been black magic.  Implement support for the SBC-3
Thin Provisioning VPD page and set the TPWS bit.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>