ARM: imx: cpuidle-imx5: Include "cpuidle.h" header file

The following build warning is seen with W=1:

warning: no previous prototype for ‘imx5_cpuidle_init’
[-Wmissing-prototypes] int __init imx5_cpuidle_init(void)

Fix this warning by including "cpuidle.h".
Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/cpuidle-imx5.c

@@ -9,6 +9,7 @@
 #include <linux/cpuidle.h>
 #include <linux/module.h>
 #include <asm/system_misc.h>
+#include "cpuidle.h"
 
 static int imx5_cpuidle_enter(struct cpuidle_device *dev,
 			      struct cpuidle_driver *drv, int index)