Add missing files to Makefile

Some .h files that were added were missed in this Makefile. Since
they are .h files, their being missing only resulted in them
disappeared from the dist archive.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Allan Jude <allan@klarasystems.com>
Closes #11705