scsi: qla2xxx: Handle PCIe error for driver

Driver will perform following

- Set PFLG_DRIVER_REMOVING flag and do not disable PCIe error reporting
  during adapter shutdown.
- If PCIe device count is already zero, return correct error type from
  PCI error interface.
- When device is offline, return correct error type from PCIe error
  path.
- If there is board disable thread active during shutdown and PCIe
  device count is zero then cancel scheduling board disable thread
  during shutdown and return.

Signed-off-by: Sawan Chandak <sawan.chandak@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>