Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Add missing ofw_bus_if.h to SRCS.

Submitted by: joerg

Port NetBSD auxio driver. The driver was modified to use led(4) and can
be used to announce various system activity.
The auxio device provides auxiliary I/O functions and is found on various
SBus/EBus UltraSPARC models. At present, only front panel LED is
controlled by this driver.

Approved by: jake (mentor)
Reviewed by: joerg
Tested by: joerg