scsi: lpfc: Fix lpfc_nvmet_mrq attribute handling when 0

Currently, when lpfc_nvmet_mrq is 0 it could mean 2 different things
depending on when its looked at. If at module load time it specifies the
default number of hardware queues to allocate, with 0 meaning default to
the number of CPUs. But post module load, a value of zero means to disable
mrq use.

Changed the driver so that enablement of mrq is based on whether nvme
target mode is enabled or not. When enabled, mrq is enabled.  Thus, the
cfg_nvemt_mrq field only specifies the number of mrq queues to enable, with
0 defaulting to the number of cpus.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>