doc: Add Latency analysis for IRQ Handlers section in the user guide

doc: Add Latency analysis for IRQ Handlers section in the user guide

Change-Id: I3040282020ad62c358c12ba1c9a5d701ffb4bb4c
Signed-off-by: Jean-Christian Kouame <jean-christian.kouame@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/97598
Reviewed-by: Mikael Ferland <mikael.ferland@ericsson.com>
Reviewed-by: Loic Prieur-Drevon <loic.prieurdrevon@gmail.com>
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>