irqbalance: new package

Irqbalance is a daemon to help balance the cpu load generated by
interrupts across all of a systems cpus.

[Thomas:
 - Add upstream URL in Config.in help text.
 - Fix indentation of init script.]

Signed-off-by: Karoly Kasza <kaszak@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>