scsi: fnic: added timestamp reporting in fnic debug stats

Added the timestamps for
1. current timestamp
2. last fnic stats read timestamp
3. last fnic stats reset timestamp
and the deltas since last stats read and last reset in fnic stats.
fnic stats uses debugfs

Signed-off-by: Sesidhar Baddela <sebaddel@cisco.com>
Signed-off-by: Satish Kharat <satishkh@cisco.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>