KernelAnalysis: Use CPUs CoreAttributes to store "Status"

KernelAnalysis: Use CPUs CoreAttributes to store "Status"

CPUs core attributes were not used to store interval data, this
leads to useless NullStateValue intervals ranging from tree start
to end. This patch uses the CPUs CoreNodes to store the "Status"
fields thus reducing the number of attributes and intervals.

Change-Id: I4b7953efff14879ea2eabe72200138f9be682c09
Signed-off-by: Loïc Prieur-Drevon <loic.prieurdrevon@gmail.com>
Reviewed-on: https://git.eclipse.org/r/70770
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Tested-by: Genevieve Bastien <gbastien+lttng@versatic.net>
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>