[SCSI] hpsa: factor out driver name

Sometimes, for testing purposes (e.g. testing rmmod on a system
that normally boots using hpsa) it's nice to rename the driver
and split it into two drivers and restrict it to certain
controllers.  This makes that easier.

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