Revert "ide: unexport DISK_EVENT_MEDIA_CHANGE for ide-gd and ide-cd"

This reverts commit 7eec77a1.

Instead of leaving disk->events completely empty, we now export the
supported events again, and tell the block layer not to forward events
to user space by not setting DISK_EVENT_FLAG_UEVENT. This allows the
block layer to distinguish between devices that for which events should
be handled in kernel only, and devices which don't support any meda
change events at all.

Cc: Borislav Petkov <bp@alien8.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>