ARM: imx: add i.MX7ULP cpuidle support

This patch adds cpuidle support for i.MX7ULP, 3 cpuidle
states supported as below:

1. WFI, just ARM wfi;
2. WAIT mode, mapped to SoC's partial stop mode #3;
3. STOP mode, mapped to SoC's partial stop mode #1.

In WAIT mode, system clock and bus clock will be enabled;
In STOP mode, system clock and bus clock will be disabled.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/cpuidle-imx7ulp.c

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2016 Freescale Semiconductor, Inc.
+ * Copyright 2017-2018 NXP
+ *   Anson Huang <Anson.Huang@nxp.com>
+ */
+
+#include <linux/cpuidle.h>
+#include <linux/module.h>
+#include <asm/cpuidle.h>
+
+#include "common.h"
+#include "cpuidle.h"
+
+static int imx7ulp_enter_wait(struct cpuidle_device *dev,
+			    struct cpuidle_driver *drv, int index)
+{
+	if (index == 1)
+		imx7ulp_set_lpm(ULP_PM_WAIT);
+	else
+		imx7ulp_set_lpm(ULP_PM_STOP);
+
+	cpu_do_idle();
+
+	imx7ulp_set_lpm(ULP_PM_RUN);
+
+	return index;
+}
+
+static struct cpuidle_driver imx7ulp_cpuidle_driver = {
+	.name = "imx7ulp_cpuidle",
+	.owner = THIS_MODULE,
+	.states = {
+		/* WFI */
+		ARM_CPUIDLE_WFI_STATE,
+		/* WAIT */
+		{
+			.exit_latency = 50,
+			.target_residency = 75,
+			.enter = imx7ulp_enter_wait,
+			.name = "WAIT",
+			.desc = "PSTOP2",
+		},
+		/* STOP */
+		{
+			.exit_latency = 100,
+			.target_residency = 150,
+			.enter = imx7ulp_enter_wait,
+			.name = "STOP",
+			.desc = "PSTOP1",
+		},
+	},
+	.state_count = 3,
+	.safe_state_index = 0,
+};
+
+int __init imx7ulp_cpuidle_init(void)
+{
+	return cpuidle_register(&imx7ulp_cpuidle_driver, NULL);
+}