Add the ability to uninitialize

zpool initialize functions well for touching every free byte...once.
But if we want to do it again, we're currently out of luck.

So let's add zpool initialize -u to clear it.

Co-authored-by: Rich Ercolani <rincebrain@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #12451 
Closes #14873

include/sys/fs/zfs.h

@@ -1265,6 +1265,7 @@ typedef enum pool_initialize_func {
 	POOL_INITIALIZE_START,
 	POOL_INITIALIZE_CANCEL,
 	POOL_INITIALIZE_SUSPEND,
+	POOL_INITIALIZE_UNINIT,
 	POOL_INITIALIZE_FUNCS
 } pool_initialize_func_t;
 

include/sys/vdev_initialize.h

@@ -33,6 +33,7 @@ extern "C" {
 #endif
 
 extern void vdev_initialize(vdev_t *vd);
+extern void vdev_uninitialize(vdev_t *vd);
 extern void vdev_initialize_stop(vdev_t *vd,
     vdev_initializing_state_t tgt_state, list_t *vd_list);
 extern void vdev_initialize_stop_all(vdev_t *vd,