psci: Add support for PSCI_CPU_SUSPEND

arm: PSCI: Add a function to return the PSCI conduit.

Arm: Add support for SMC Calling Convention

Arm DEN0028 defines a calling mechanism used with Secure Monitor Call (SMC)
and Hypervisor Call (HVC) instructions. To discover SMCCC, we must:

1) Find

Arm: Add support for SMC Calling Convention

Arm DEN0028 defines a calling mechanism used with Secure Monitor Call (SMC)
and Hypervisor Call (HVC) instructions. To discover SMCCC, we must:

1) Find the PSCI conduit (either via ACPI FADT, or Device Tree)
2) Use PSCI_VERSION to determine whether PSCI_FEATURES is supported
3) Call PSCI_FEATURES with SMCCC_VERSION to determine the implementation
version.

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Add function that returns true if PSCI has been initialized

Add support for ARM Power State Coordination Interface (PSCI).