Support device deletion via sysfs.

I.e: echo 1 > /sys/block/sd<X>/device/delete

Link: https://lore.kernel.org/r/159622929885.30579.2727491506675011534.stgit@brunhildaReviewed-by: Scott Teel <scott.teel@microsemi.com>
Reviewed-by: Scott Benesh <scott.benesh@microsemi.com>
Reviewed-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Kevin Barnett <kevin.barnett@microsemi.com>
Signed-off-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>