scsi: qla2xxx: Add ql2xiniexchg parameter

Previously, the ql2xexchoffld module parameter was used to control the
max number of exchanges to be offload onto host memory.

Module parameter ql_dm_tgt_ex_pct was used to control the percentage of
exchanges allocated to the Target side.

With this patch, module parameter ql_dm_tgt_ex_pct is no longer used to
control exchanges for the driver. New module parameter ql2xiniexchg is
added to control exchanges between target mode and initiator mode.

With the updated module parameters, users can control the exact number
of exchanges for either Initiator or Target. The exchange offload
feature will be automatically enabled when the total number of exchanges
exceeds 2048 limit.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>