zio: update ZIO type x stage documentation
- add column for TRIM ZIOs
- remove R from ZIO_STAGE_ISSUE_ASYNC, never happened
- remove I from ZIO_STAGE_VDEV_IO_DONE, never happened
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #15959