MFC r349321: Improve AHCI Enclosure Management and SES interoperation.

Since SES specs do not define mechanism to map enclosure slots to SATA
disks, AHCI EM code I written many years ago appeared quite useless,
that always bugged me. I was thinking whether it was a good idea, but
if LSI HBAs do that, why I shouldn't?

This change introduces simple non-standard mechanism for the mapping
into both AHCI EM and SES code, that makes AHCI EM on capable controllers
(most of Intel's) a first-class SES citizen, allowing it to report disk
physical path to GEOM, show devices inserted into each enclosure slot in
`sesutil map` and `getencstat`, control locate and fault LEDs for specific
devices with `sesutil locate adaX on` and `sesutil fault adaX on`, etc.

I've successfully tested this on Supermicro X10DRH-i motherboard connected
with sideband cable of its S-SATA Mini-SAS connector to SAS815TQ backplane.
It can indicate with LEDs Locate, Fault and Rebuild/Remap SES statuses for
each disk identical to real SES of Supermicro SAS2 backplanes.

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 API to obtain primary enclosure name and ID for /dev/sesX devices.

sesX device number may change between reboots, so to properly identify
the instance we need more data. Name and ID reported here may mach ones
reported by SCSI device, but that is not really required by specs.

MFC after: 1 week
Sponsored by: iXsystems, Inc.

MFprojects/zfsd:
Revamp the CAM enclosure services driver.
This updated driver uses an in-kernel daemon to track state changes and
publishes physical path location information\for disk elements into the
CAM device database.

Sponsored by: Spectra Logic Corporation
Sponsored by: iXsystems, Inc.
Submitted by: gibbs, will, mav