[core/sched/cbs] Bugfix FTrace flags on 64bit architectures

Dumping flags as chars corrupts the event formatting, this patch switch to
usage of strings which are working well on 64bit systems as well.

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[core/sched/cbs] Bugfix Rt upper-bound to stick in 32bit

The previous definition produce a 0 value for the Rt upper bound, with
a corresponding misbehavior on round time clamping.

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[core/sched/cbs] Cosmetics

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[core/sched/cbs] Add type checking for some constants

If these constants are defined with a wrong data-type an overflow could
happens and the values becomes null. This condition is checked at

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[core/sched/cbs] Bugfix dump of signed values

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[core/sched/cbs] Report null Rt error on first round

At the really first round, the Rt is null and that should be the round error
as well.

Signed-off-by: Patrick Bellasi <derkling@gmail.com>