[SCSI] megaraid_sas: Add the support for updating the OS after adding/removing the devices from FW

Driver will update the OS devices after adding and deleting the device
from FW.  When driver receive add or delete AEN from FW, driver will
send the DCMD cmd to get the System PD list from FW.  Then driver will
check if this device already in the OS: If add event and OS don't have
the device (but it is in the list), driver add the device to OS,
otherwise driver will not add.  If remove event, driver will check the
list, if is not in the list, but OS have the device, driver will
remove the device.

Signed-off-by Bo Yang<bo.yang@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>