ceph: show tasks waiting on caps in debugfs caps file

Add some visibility of tasks that are waiting for caps to the "caps"
debugfs file. Display the tgid of the waiting task, inode number, and
the caps the task needs and wants.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>