arm64: dts: exynos: Add cpu_suspend property of PSCI for exynos5433

arm64: dts: exynos: Add cpu_suspend property of PSCI for exynos5433

The ARM64 Exynos5433 supports PSCI(Power State Coordinate Interface)[1] v0.1.
When PSCI v0.1 is used, the device-tree should contain the specific entry
point such as cpu_suspend. Add the 'cpu_suspend' property in order to
support the cpuidle and suspend execution on Exynos5433 SoC.

The 'cpu_suspend' of psci is originally intended for use in idle subsystems.
Although the cpuidle and suspend-to-RAM framework have separate routine
in order to enter the low-power state, PSCI v0.1 doesn't support
the separate the entry point such as 'system_suspend' on PSCI v1.0.

So, the 'cpu_suspend' of PSCI v0.1 on Exynos5433 is used for both
cpuidle and suspend-to-RAM.

[1] http://infocenter.arm.com/help/topic/com.arm.doc.den0022d/Power_State_Coordination_Interface_PDD_v1_1_DEN0022D.pdf

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>