[COMMON] arm64: psci: Reappear psci_power_state_pack

[COMMON] arm64: psci: Reappear psci_power_state_pack

psci_power_state_pack which combines PSCI power state information
to integer is removed by commit c8cc427("arm64: psci: kill
psci_power_state").

In case of exynos, it needs to reconstitute PSCI power state to
support extra power mode which cpuidle does not support. To
resonstitute PSCI power state, psci_power_state_pack is added.
It will be used in psci_suspend_customized_finisher.

Change-Id: I506e690965e73cdd1d6acee7664b5cf4cfc049a0
Signed-off-by: Park Bumgyu <bumgyu.park@samsung.com>