KVM: ARM: Power State Coordination Interface implementation

Implement the PSCI specification (ARM DEN 0022A) to control
virtual CPUs being "powered" on or off.

PSCI/KVM is detected using the KVM_CAP_ARM_PSCI capability.

A virtual CPU can now be initialized in a "powered off" state,
using the KVM_ARM_VCPU_POWER_OFF feature flag.

The guest can use either SMC or HVC to execute a PSCI function.

Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>

Documentation/virtual/kvm/api.txt

@@ -2185,6 +2185,10 @@ return ENOEXEC for that vcpu.
 Note that because some registers reflect machine topology, all vcpus
 should be created before this ioctl is invoked.
 
+Possible features:
+	- KVM_ARM_VCPU_POWER_OFF: Starts the CPU in a power-off state.
+	  Depends on KVM_CAP_ARM_PSCI.
+
 
 4.78 KVM_GET_REG_LIST