arm64: add support for ACPI Low Power Idle(LPI)

This patch adds appropriate callbacks to support ACPI Low Power Idle
(LPI) on ARM64.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

arch/arm64/kernel/cpuidle.c

@@ -9,6 +9,9 @@
  * published by the Free Software Foundation.
  */
 
+#include <linux/acpi.h>
+#include <linux/cpuidle.h>
+#include <linux/cpu_pm.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
 
@@ -39,3 +42,18 @@ int arm_cpuidle_suspend(int index)
 
 	return cpu_ops[cpu]->cpu_suspend(index);
 }
+
+#ifdef CONFIG_ACPI
+
+#include <acpi/processor.h>
+
+int acpi_processor_ffh_lpi_probe(unsigned int cpu)
+{
+	return arm_cpuidle_init(cpu);
+}
+
+int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
+{
+	return CPU_PM_CPU_IDLE_ENTER(arm_cpuidle_suspend, lpi->index);
+}
+#endif