[COMMON] arm64: kernel: Support customized suspend finisher

[COMMON] arm64: kernel: Support customized suspend finisher

We hope that PSCI framework cover the all platform specific power
states, unfortunately PSCI can support only state managed by cpuidle.
Hence it is not correspond on Exynos.

psci_suspend_customized_finisher supports extra power state which
cpuidle does not handle such as system sleep, system idle clock
down and cluster power down.

Change-Id: I970f5ec2477de8e3fea2e10528bfc564b584c144
Signed-off-by: Park Bumgyu <bumgyu.park@samsung.com>
Signed-off-by: Youngtae Lee <yt0729.lee@samsung.com>