The driver allocates a sg list per io struture based on a fixed maximum
size. When it registers with the protocol transports and indicates the max sg
list size it supports, the driver manipulates the fixed value to report a
lesser amount so that it has reserved space for sg elements that are used for
DIF.

The driver initialization path sets the cfg_sg_seg_cnt field to the
manipulated value for scsi. NVME initialization ran afterward and capped it's
maximum by the manipulated value for SCSI. This erroneously made NVME report
the SCSI-reduce-for-DIF value that reduced the max io size for nvme and wasted
sg elements.

Rework the driver so that cfg_sg_seg_cnt becomes the overall maximum size and
allow the max size to be tunable.  A separate (new) scsi sg count is then
setup with the scsi-modified reduced value. NVME then initializes based off
the overall maximum.
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>