ext4: convert ext4_fc_track_dentry type events to use event class

ext4: convert ext4_fc_track_dentry type events to use event class

One should use DECLARE_EVENT_CLASS for similar event types instead of
defining TRACE_EVENT for each event type. This is helpful in reducing
the text section footprint for e.g. [1]

[1]: https://lwn.net/Articles/381064/

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/a019cb46219ef4b30e4d98d7ced7d8819a2fc61d.1647057583.git.riteshh@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>