ARC: [plat-eznps] remove IPI clear from SMP operations
Today we register to plat_smp_ops.clear() method which actually
is acking the IPI.
However this is already taking care by our irqchip driver specifically
by the irq_chip.irq_eoi() method.
This is perfect timing where it should be done and no special handling
is needed at plat_smp_ops.clear().