isci: fix interrupt disable

There is a (dubious?) lost irq workaround in sci_controller_isr() that
effectively nullifies attempts to disable interrupts.  Until the
workaround can be re-evaluated add some infrastructure to prevent the
interrupt handler from inadvertantly re-enabling interrupts.

The failure mode was interrupts continuing to run after the driver had
been removed and its iomappings torn down.

Reported-by: Jacek Danecki <jacek.danecki@intel.com>
Tested-by: Jacek Danecki <jacek.danecki@intel.com>
[richard: clear remaining interrupts at the end of reset]
Acked-by: Richard Boyd <richard.g.boyd@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/scsi/isci/host.h b/drivers/scsi/isci/host.h
index 9dc910b..9701c1d 100644
--- a/drivers/scsi/isci/host.h
+++ b/drivers/scsi/isci/host.h
@@ -200,6 +200,7 @@
 	struct pci_dev *pdev;
 	#define IHOST_START_PENDING 0
 	#define IHOST_STOP_PENDING 1
+	#define IHOST_IRQ_ENABLED 2
 	unsigned long flags;
 	wait_queue_head_t eventq;
 	struct Scsi_Host *shost;