fix irq stats sorting

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
cleanup: pre-compute irq stats

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
remove the detailled historic graph

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>