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

include/os/linux/spl/sys/procfs_list.h

@@ -57,6 +57,7 @@ typedef struct procfs_list_node {
 } procfs_list_node_t;
 
 void procfs_list_install(const char *module,
+    const char *submodule,
     const char *name,
     mode_t mode,
     procfs_list_t *procfs_list,