A practical LART is to know beforehand when some out-of-band work is
about to run on a non-isolated CPU, so that the application may warn
the user about the potentially higher latency figures induced by
higher rates of cache and TLB misses which may be caused by heavy
in-band load running on the same core.

The control device now accepts the
[oob_]ioctl(EVL_CTLIOC_GET_CPUSTATE) request, which queries the
current state of a CPU:

- EVL_CPU_ISOL if it does not belong to housekeeping set of the
  in-band kernel, i.e. not mentioned in isolcpus= for the scheduling
  domain.

- EVL_CPU_OOB if it is part of the out-of-band set EVL manages.

- EVL_CPU_OFFLINE if currently off.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>