FreeBSD: Add support for procfs_list

The procfs_list interface is required by several kstats. Implement
this functionality for FreeBSD to provide access to these kstats.
                           
Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #10890

lib/libzpool/kernel.c

@@ -444,6 +444,7 @@ seq_printf(struct seq_file *m, const char *fmt, ...)
 
 void
 procfs_list_install(const char *module,
+    const char *submodule,
     const char *name,
     mode_t mode,
     procfs_list_t *procfs_list,