isci: preallocate requests

the dma_pool interface is optimized for object_size << page_size which
is not the case with isci_request objects and the dma_pool routines show
up in the top of the profile.

The old io_request_table which tracked whether tci slots were in-flight
or not is replaced with an IREQ_ACTIVE flag per request.

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

diff --cc drivers/scsi/isci/host.c
Simple merge

diff --cc drivers/scsi/isci/host.h
Simple merge

diff --cc drivers/scsi/isci/remote_device.c
Simple merge

diff --cc drivers/scsi/isci/request.c
Simple merge

diff --cc drivers/scsi/isci/request.h
Simple merge

diff --cc drivers/scsi/isci/task.c
Simple merge