libnvdimm, pmem: Add sysfs notifications to badblocks

Sysfs "badblocks" information may be updated during run-time that:
 - MCE, SCI, and sysfs "scrub" may add new bad blocks
 - Writes and ioctl() may clear bad blocks

Add support to send sysfs notifications to sysfs "badblocks" file
under region and pmem directories when their badblocks information
is re-evaluated (but is not necessarily changed) during run-time.

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Linda Knippers <linda.knippers@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/pmem.h

@@ -17,6 +17,7 @@ struct pmem_device {
 	size_t			size;
 	/* trim size when namespace capacity has been section aligned */
 	u32			pfn_pad;
+	struct kernfs_node	*bb_state;
 	struct badblocks	bb;
 	struct dax_device	*dax_dev;
 	struct gendisk		*disk;