ARM: imx: add cpuidle support for i.mx6ul

This patch enables cpuidle driver for i.MX6UL, it
reuses i.MX6SX's cpuidle driver, 3 levels of cpuidle
supported:

1. ARM WFI;
2. SOC in WAIT mode;
3. SOC in WAIT mode + ARM power off.

As i.MX6UL has cortex-A7 CORE with an internal L2
cache, so flushing it before powering down ARM platform
is necessary, flush_cache_all() in last step of cpu_suspend
has very small overhead, just call it to avoid cache
type check for different platforms.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/cpuidle-imx6sx.c

@@ -9,6 +9,7 @@
 #include <linux/cpuidle.h>
 #include <linux/cpu_pm.h>
 #include <linux/module.h>
+#include <asm/cacheflush.h>
 #include <asm/cpuidle.h>
 #include <asm/suspend.h>
 
@@ -17,6 +18,15 @@
 
 static int imx6sx_idle_finish(unsigned long val)
 {
+	/*
+	 * for Cortex-A7 which has an internal L2
+	 * cache, need to flush it before powering
+	 * down ARM platform, since flushing L1 cache
+	 * here again has very small overhead, compared
+	 * to adding conditional code for L2 cache type,
+	 * just call flush_cache_all() is fine.
+	 */
+	flush_cache_all();
 	cpu_do_idle();
 
 	return 0;

arch/arm/mach-imx/mach-imx6ul.c

@@ -16,6 +16,7 @@
 #include <asm/mach/map.h>
 
 #include "common.h"
+#include "cpuidle.h"
 
 static void __init imx6ul_enet_clk_init(void)
 {
@@ -79,6 +80,8 @@ static void __init imx6ul_init_irq(void)
 
 static void __init imx6ul_init_late(void)
 {
+	imx6sx_cpuidle_init();
+
 	if (IS_ENABLED(CONFIG_ARM_IMX6Q_CPUFREQ))
 		platform_device_register_simple("imx6q-cpufreq", -1, NULL, 0);
 }