sr: implement sr_check_events()

Replace sr_media_change() with sr_check_events().  It normally only
uses GET_EVENT_STATUS_NOTIFICATION to check both media change and
eject request.  If @clearing includes DISK_EVENT_MEDIA_CHANGE, it
issues TUR and compares whether media presence has changed.  The SCSI
specific media change uevent is kept for compatibility.

sr_media_change() was doing both media change check and revalidation.
The revalidation part is split into sr_block_revalidate_disk().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index 216af85..8675861 100644
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -104,6 +104,7 @@
 #define UNMAP		      0x42
 #define READ_TOC              0x43
 #define READ_HEADER           0x44
+#define GET_EVENT_STATUS_NOTIFICATION 0x4a
 #define LOG_SELECT            0x4c
 #define LOG_SENSE             0x4d
 #define XDWRITEREAD_10        0x53