scsi: add topology support

Export the physical block size in the READ CAPACITY (16) command,
and add the new block limits VPD page to export the minimum and
optiomal I/O sizes.

Note that we also need to bump the scsi revision level to SPC-2
as that is the minimum requirement by at least the Linux kernel
to try READ CAPACITY (16) first and look at the block limits VPD
page.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
