Our current TRIM payload is a single sector that can accommodate 64 *
65535 blocks being unmapped.  Report this value in the Block Limits
Maximum Unmap LBA count field.

If a storage device supports TRIM and the DRAT and RZAT bits are set,
report TPRZ=1 in Read Capacity(16).
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>