kernel: Disable IRQ time accounting

kernel: Disable IRQ time accounting

This feature is now disabled (was disabled on ARM before) as we do not
need it:

"Select this option to enable fine granularity task irq time accounting.
This is done by reading a timestamp on each transitions between softirq
and hardirq state, so there can be a small performance impact."

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
Acked-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>