Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r234458, r234603, r234610, r234727, r234816, r234848, r234868,
r234869, r234899, r234940, r234993, r234994, r235071 -c r235076, r235080,
r235096:
- Add support for the DDF metadata format, as defined by the SNIA Common
RAID Disk Data Format Specification v2.0;
- Add support for reading non-degraded RAID4/5/5E/5EE/5R/6/MDF volumes.

Sponsored by: iXsystems, Inc.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

MFgraid/head:
Add new RAID GEOM class, that is going to replace ataraid(4) in supporting
various BIOS-based software RAIDs. Unlike ataraid(4) this implementation
does not depend on legacy ata(4) subsystem and can be used with any disk
drivers, including new CAM-based ones (ahci(4), siis(4), mvs(4), ata(4)
with `options ATA_CAM`). To make code more readable and extensible, this
implementation follows modular design, including core part and two sets
of modules, implementing support for different metadata formats and RAID
levels.

Support for such popular metadata formats is now implemented:
Intel, JMicron, NVIDIA, Promise (also used by AMD/ATI) and SiliconImage.

Such RAID levels are now supported:
RAID0, RAID1, RAID1E, RAID10, SINGLE, CONCAT.

For any all of these RAID levels and metadata formats this class supports
full cycle of volume operations: reading, writing, creation, deletion,
disk removal and insertion, rebuilding, dirty shutdown detection
and resynchronization, bad sector recovery, faulty disks tracking,
hot-spare disks. For Intel and Promise formats there is support multiple
volumes per disk set.

Look graid(8) manual page for additional details.

Co-authored by: imp
Sponsored by: Cisco Systems, Inc. and iXsystems, Inc.