linux-wandboard

tile: various minor cleanups to hardwall subsystem

First, clean up active hardwalls in exit_thread().  This is a better
place than in arch_release_thread_info().

Second, mask out any non-online cpus from the cpumask after
validating any required semantics of the cpu set.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>