Add prototypes

Add prototypes/move prototypes to header files.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10470

module/os/freebsd/zfs/spa_os.c

@@ -37,6 +37,7 @@
 #include <sys/zil.h>
 #include <sys/ddt.h>
 #include <sys/vdev_impl.h>
+#include <sys/vdev_os.h>
 #include <sys/vdev_removal.h>
 #include <sys/vdev_indirect_mapping.h>
 #include <sys/vdev_indirect_births.h>
@@ -72,9 +73,6 @@
 #include "zfs_prop.h"
 #include "zfs_comutil.h"
 
-extern int vdev_geom_read_pool_label(const char *name, nvlist_t ***configs,
-    uint64_t *count);
-
 static nvlist_t *
 spa_generate_rootconf(const char *name)
 {