arm64: add CPU_HOTPLUG infrastructure

This patch adds the basic infrastructure necessary to support
CPU_HOTPLUG on arm64, based on the arm implementation. Actual hotplug
support will depend on an implementation's cpu_operations (e.g. PSCI).

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --cc arch/arm64/Kconfig
Simple merge

diff --cc arch/arm64/include/asm/cpu_ops.h
Simple merge

diff --cc arch/arm64/include/asm/irq.h
Simple merge

diff --cc arch/arm64/include/asm/smp.h
Simple merge

diff --cc arch/arm64/kernel/cputable.c
Simple merge

diff --cc arch/arm64/kernel/irq.c
Simple merge

diff --cc arch/arm64/kernel/process.c
Simple merge

diff --cc arch/arm64/kernel/smp.c
Simple merge