MFC rr222039:

MFC rr222039:
Add support for "LED" enclosure management messages, defined by the AHCI.

When supported by hardware, this allows to control per-port activity, locate
and fault LEDs via the led(4) API for localization and status reporting
purposes. Supporting AHCI controllers may transmit that information to the
backplane controllers via SGPIO interface. Backplane controllers interpret
received statuses in some way (IBPI standard) to report them using present
indicators.

git-svn-id: svn://svn.freebsd.org/base/stable/8@222916 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f