firewire: sbp2: add support for disks >2 TB (and 16 bytes long CDBs)

Increase the command ORB data structure to transport up to 16 bytes long
CDBs (instead of 12 bytes), and tell the SCSI mid layer about it.  This
is notably necessary for READ CAPACITY(16) and friends, i.e. support of
large disks.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>