[SCSI] hpsa: Increase the number of scatter gather elements supported.

This uses the scatter-gather chaining feature of Smart Array
controllers.  32 scatter-gather elements are embedded in the
"command list", and the last element in the list may be marked
as a "chain pointer", and point to an additional block of
scatter gather elements.  The precise number of scatter gather
elements supported is dependent on the particular kind of
Smart Array, and is determined at runtime by querying the
hardware.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>