[SCSI] aic94xx: plumb in I_T_nexus_reset task management function

Currently aic94xx has no exported I_T_nexus_reset function.  This is a
bit of a huge problem, since sas_ata relies on this function to
perform an ATA phy reset and also it means that if abort fails, we
really have no bigger hammer to hit everything with.

Plumb in the I_T_nexus_reset by quiescing the sequencer, sending the
correct phy reset (link for ATA and hard for SAS) and then carefully
resuming the sequencer again.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>