irqchip/armada-xp: Consolidate hotplug state space

The mpic is either the main interrupt controller or is cascaded behind a
GIC. The mpic is single instance and the modes are mutually exclusive, so
there is no reason to have seperate cpu hotplug states.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Link: http://lkml.kernel.org/r/20161221192112.333161745@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>