zed: mark disks as REMOVED when they are removed

ZED does not take any action for disk removal events if there is no
spare VDEV available. Added zpool_vdev_remove_wanted() in libzfs
and vdev_remove_wanted() in vdev.c to remove the VDEV through ZED
on removal event.  This means that if you are running zed and
remove a disk, it will be propertly marked as REMOVED.

Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>

include/os/linux/spl/sys/Makefile.am

@@ -20,6 +20,7 @@ KERNEL_H = \
 	kmem.h \
 	kstat.h \
 	list.h \
+	misc.h \
 	mod_os.h \
 	mutex.h \
 	param.h \

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

@@ -0,0 +1,29 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or https://opensource.org/licenses/CDDL-1.0.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+#ifndef _OS_LINUX_SPL_MISC_H
+#define	_OS_LINUX_SPL_MISC_H
+
+#include <linux/kobject.h>
+
+extern void spl_signal_kobj_evt(struct block_device *bdev);
+
+#endif