megaraid_sas: Do not allow PCI access during OCR

This patch will do synhronization between OCR function and AEN function
using "reset_mutex" lock.  reset_mutex will be acquired only in the
first half of the AEN function which issues a DCMD. Second half of the
function which calls SCSI API (scsi_add_device/scsi_remove_device)
should be out of reset_mutex to avoid deadlock between scsi_eh thread
and driver.

During chip reset (inside OCR function), there should not be any PCI
access and AEN function (which is called in delayed context) may be
firing DCMDs (doing PCI writes) when chip reset is happening in parallel
which will cause FW fault. This patch will solve the problem by making
AEN thread and OCR thread mutually exclusive.

Signed-off-by: Sumit Saxena <sumit.saxena@avagotech.com>
Signed-off-by: Kashyap Desai <kashyap.desai@avagotech.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>