mpt2sas: Clear PFA Status on SGPIO when PFA Drive is Removed or Replaced

Added code to send a SEP message that turns off the Predictive
Failure LED when a drive is removed (if Predictive Failure LED was turned on).

Added a new flag 'pfa_led_on' per device that tracks the status of Predictive
Failure LED. When the drive is removed, this flag is checked and
sends the SEP message to turn off the respective Predictive Failure LED.

Signed-off-by: Sreekanth Reddy <Sreekanth.Reddy@avagotech.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>