arm64/cpuinfo: Make hotplug notifier symmetric

There is no requirement to keep the sysfs files around until the CPU is
completely dead. Remove them during the DOWN_PREPARE notification. This is
a preparatory patch for converting to the hotplug state machine.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: rt@linutronix.de
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20161126231350.10321-16-bigeasy@linutronix.de


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