can't do a timeout bigger than 15 seconds. The code wasn't checking for
this and because bitmasking was involved the requested timeout was
basically adjusted modulo-16. That led to things like a 128 second
timeout actually being a 9 second timeout, which accidentally worked fine
until watchdogd was changed to only pet the dog once every 10 seconds.
to check the status property in their probe routines.
Simplebus used to only instantiate its children whose status="okay"
but that was improper behavior, fixed in r261352. Now that it doesn't
check anymore and probes all its children; the children all have to
do the check because really only the children know how to properly
interpret their status property strings.
Right now all existing drivers only understand "okay" versus something-
that's-not-okay, so they all use the new ofw_bus_status_okay() helper.
