Enhanced Interrupt API

We now implemented Altera's vic as External Interrupt Controller(eic). And now we can make use of the enhanced interrupt api.

If you use the vic you don't need to tell your ISR that it is interruptible by software anymore.

You have to set the preemption options in the bsp in order to manage that interrupts are interruptible.

So in your software you don't need to worry about calling alt_irq_interruptible() and alt_irq_non_interruptible() the right way.

But I've only used the VIC for some days and will examine it a bit more......