MFC r239545:

MFC r239545:

  Fix/add isci(4) support for SCSI UNMAP to ATA DSM translation.

  This addresses kernel panic observed when sending SCSI UNMAP
  commands to SATA disks attached to isci(4).

  1) Flesh out callback routines to allocate/free buffers needed for
     translating SCSI UNMAP data to ATA DSM data.
  2) Add controller-level pool for storing buffers previously allocated
     for UNMAP translation, to lessen chance of no buffer available
     under memory pressure.
  3) Ensure driver properly handles case where buffer pool is empty
     and contigmalloc returns NULL.

Sponsored by:	Intel
Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/releng/9.1@239741 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f