ARM: imx: ARM: imx: include cpuidle.h rather than mach/cpuidle.h

Rename mach-imx/include/mach/cpuidle.h to mach-imx/cpuidle.h, and
update users to include cpuidle.h rather than mach/cpuidle.h.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>