scsi: qla2xxx: Add debug knob for user control workload

For Target mode, user can control the work load by placing qla2xxx's irq
vector on certain CPU via the smp_affinity knob. This patch allows user
to control the number of QPair's irq to be active. The irqs are
allocated at driver load time until unload. The work itself is placed on
the QPair based on user setting.

Usage:
  modprobe qla2xxx qlini_mode=disabled ql2xuctrlirq=1
  mount -t debugfs none /sys/kernel/debug
  echo 2 > /sys/kernel/debug/qla2xxx/qla2xxx_[host num]/naqp
  echo [cpu id] > /proc/irq/[irq id]/smp_affinity_list

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>