arm64: kernel: introduce cpu_init_idle CPU operation

arm64: kernel: introduce cpu_init_idle CPU operation

The CPUidle subsystem on ARM64 machines requires the idle states
implementation back-end to initialize idle states parameter upon
boot. This patch adds a hook in the CPU operations structure that
should be initialized by the CPU operations back-end in order to
provide a function that initializes cpu idle states.

This patch also adds the infrastructure to arm64 kernel required
to export the CPU operations based initialization interface, so
that drivers (ie CPUidle) can use it when they are initialized
at probe time.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit d64f84f696463c58e1908510e45b0f5d450f737a)
Signed-off-by: Mark Brown <broonie@kernel.org>
Conflicts:
	arch/arm64/kernel/Makefile