pm: Add power management states definition

Add definition power management states, these states were inspired by
ACPI specification. This commit is part of the following pr
https://github.com/zephyrproject-rtos/zephyr/pull/27315 from Wentong.

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>

include/power/power.h

@@ -8,6 +8,7 @@
 #define ZEPHYR_INCLUDE_POWER_POWER_H_
 
 #include <zephyr/types.h>
+#include <power/power_state.h>
 #include <stdbool.h>
 
 #ifdef __cplusplus

include/power/power_state.h

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2020 Intel corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_POWER_POWER_STATE_H_
+#define ZEPHYR_INCLUDE_POWER_POWER_STATE_H_
+
+#include <sys/util.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @defgroup pm_states Power Management states
+ * @{
+ */
+
+/**
+ * @enum pm_state Power management state
+ */
+enum pm_state {
+	/**
+	 * @brief Runtime active state
+	 *
+	 * The system is fully powered and active.
+	 *
+	 * @note This state is correlated with ACPI G0/S0 state
+	 */
+	PM_STATE_ACTIVE,
+	/**
+	 * @brief Runtime idle state
+	 *
+	 * Runtime idle is a system sleep state in which all of the cores
+	 * enter deepest possible idle state and wait for interrupts, no
+	 * requirements for the devices, leaving them at the states where
+	 * they are.
+	 *
+	 * @note This state is correlated with ACPI S0ix state
+	 */
+	PM_STATE_RUNTIME_IDLE,
+	/**
+	 * @brief Suspend to idle state
+	 *
+	 * The system goes through a normal platform suspend where it puts
+	 * all of the cores in deepest possible idle state and *may* puts peripherals
+	 * into low-power states. No operating state is lost (ie. the cpu core
+	 * does not lose execution context), so the system can go back to where
+	 * it left off easily enough.
+	 *
+	 * @note This state is correlated with ACPI S1 state
+	 */
+	PM_STATE_SUSPEND_TO_IDLE,
+	/**
+	 * @brief Standby state
+	 *
+	 * In addition to putting peripherals into low-power states all
+	 * non-boot CPUs are powered off. It should allow more energy to be
+	 * saved relative to suspend to idle, but the resume latency will
+	 * generally be greater than for that state. But it should be the same
+	 * state with suspend to idle state on uniprocesser system.
+	 *
+	 * @note This state is correlated with ACPI S2 state
+	 */
+	PM_STATE_STANDBY,
+	/**
+	 * @brief Suspend to ram state
+	 *
+	 * This state offers significant energy savings by powering off as much
+	 * of the system as possible, where memory should be placed into the
+	 * self-refresh mode to retain its contents. The state of devices and
+	 * CPUs is saved and held in memory, and it may require some boot-
+	 * strapping code in ROM to resume the system from it.
+	 *
+	 * @note This state is correlated with ACPI S3 state
+	 */
+	PM_STATE_SUSPEND_TO_RAM,
+	/**
+	 * @brief Suspend to disk state
+	 *
+	 * This state offers significant energy savings by powering off as much
+	 * of the system as possible, including the memory. The contents of
+	 * memory are written to disk or other non-volatile storage, and on resume
+	 * it's read back into memory with the help of boot-strapping code,
+	 * restores the system to the same point of execution where it went to
+	 * suspend to disk.
+	 *
+	 * @note This state is correlated with ACPI S4 state
+	 */
+	PM_STATE_SUSPEND_TO_DISK,
+	/**
+	 * @brief Soft off state
+	 *
+	 * This state consumes a minimal amount of power and requires a large
+	 * latency in order to return to runtime active state. The contents of
+	 * system(CPU and memory) will not be preserved, so the system will be
+	 * restarted as if from initial power-up and kernel boot.
+	 *
+	 * @note This state is correlated with ACPI G2/S5 state
+	 */
+	PM_STATE_SOFT_OFF
+};
+
+/**
+ * @}
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif