ARM: mx25: Add basic suspend/resume support

Tested basic suspend/resume on a mx25pdk:

$ echo enabled > /sys/class/tty/ttymxc0/power/wakeup
$ echo mem > /sys/power/state

Then press any key in the serial console and the system wakes up.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/Makefile

@@ -3,7 +3,7 @@ obj-y := cpu.o system.o irq-common.o
 obj-$(CONFIG_SOC_IMX1) += mm-imx1.o
 obj-$(CONFIG_SOC_IMX21) += mm-imx21.o
 
-obj-$(CONFIG_SOC_IMX25) += cpu-imx25.o mach-imx25.o
+obj-$(CONFIG_SOC_IMX25) += cpu-imx25.o mach-imx25.o pm-imx25.o
 
 obj-$(CONFIG_SOC_IMX27) += cpu-imx27.o pm-imx27.o
 obj-$(CONFIG_SOC_IMX27) += mm-imx27.o ehci-imx27.o

arch/arm/mach-imx/common.h

@@ -66,6 +66,7 @@ void imx_gpc_check_dt(void);
 void imx_gpc_set_arm_power_in_lpm(bool power_off);
 void imx_gpc_set_arm_power_up_timing(u32 sw2iso, u32 sw);
 void imx_gpc_set_arm_power_down_timing(u32 sw2iso, u32 sw);
+void imx25_pm_init(void);
 
 enum mxc_cpu_pwr_mode {
 	WAIT_CLOCKED,		/* wfi only */

arch/arm/mach-imx/mach-imx25.c

@@ -41,6 +41,7 @@ static const char * const imx25_dt_board_compat[] __initconst = {
 
 DT_MACHINE_START(IMX25_DT, "Freescale i.MX25 (Device Tree Support)")
 	.init_early	= imx25_init_early,
+	.init_late      = imx25_pm_init,
 	.init_irq	= mx25_init_irq,
 	.dt_compat	= imx25_dt_board_compat,
 MACHINE_END

arch/arm/mach-imx/pm-imx25.c

+/*
+ * Copyright 2016 NXP Semiconductors
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/suspend.h>
+#include <linux/io.h>
+
+static int imx25_suspend_enter(suspend_state_t state)
+{
+	if (!IS_ENABLED(CONFIG_PM))
+		return 0;
+
+	switch (state) {
+	case PM_SUSPEND_MEM:
+		cpu_do_idle();
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct platform_suspend_ops imx25_suspend_ops = {
+	.enter = imx25_suspend_enter,
+	.valid = suspend_valid_only_mem,
+};
+
+void __init imx25_pm_init(void)
+{
+	suspend_set_ops(&imx25_suspend_ops);
+}