Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Add optional -o argument to the `graid label ` to specify some metadata
format options. Use it for specifying byte order for the DDF metadata:
big-endian defined by specification and little-endian used by Adaptec.

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.