ARM: at91: aic can use fast eoi handler type

The Advanced Interrupt Controller allows us to use the fast EOI handler type.
It lets us remove the Atmel specific workaround into arch/arm/kernel/irq.c
used to indicate to the AIC the end of the interrupt treatment.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>