[SCSI] isci: stop interpreting ->lldd_lu_reset() as an ata soft-reset

Driving resets from libsas-eh is pre-mature as libata will make a
decision about performing a softreset.  Currently libata determines
whether to perform a softreset based on ata_eh_followup_srst_needed(),
and none of those conditions apply to isci.

Remove the srst implementation and translate ->lldd_lu_reset() for ata
devices as a request to drive a reset via libata-eh.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>