libata: Report disk alignment and physical block size

For disks with 4KB sectors, report the correct block size and alignment
when filling out the READ CAPACITY(16) response.

This patch is based upon code from Matthew Wilcox' 4KB ATA tree.  I
fixed the bug I reported a while back caused by ATA and SCSI using
different approaches to describing the alignment.

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