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 properly marked as REMOVED.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #13797

include/os/linux/kernel/linux/blkdev_compat.h

@@ -261,6 +261,32 @@ bio_set_bi_error(struct bio *bio, int error)
 #define	BIO_END_IO(bio, error)		bio_endio(bio, error);
 #endif /* HAVE_1ARG_BIO_END_IO_T */
 
+/*
+ * 5.15 MACRO,
+ *   GD_DEAD
+ *
+ * 2.6.36 - 5.14 MACRO,
+ *   GENHD_FL_UP
+ *
+ * Check the disk status and return B_TRUE if alive
+ * otherwise B_FALSE
+ */
+static inline boolean_t
+zfs_check_disk_status(struct block_device *bdev)
+{
+#if defined(GENHD_FL_UP)
+	return (!!(bdev->bd_disk->flags & GENHD_FL_UP));
+#elif defined(GD_DEAD)
+	return (!test_bit(GD_DEAD, &bdev->bd_disk->state));
+#else
+/*
+ * This is encountered if neither GENHD_FL_UP nor GD_DEAD is available in
+ * the kernel - likely due to an MACRO change that needs to be chased down.
+ */
+#error "Unsupported kernel: no usable disk status check"
+#endif
+}
+
 /*
  * 4.1 API,
  * 3.10.0 CentOS 7.x API,