ARM: imx: Enable imx53 low power idle

Add various functionality needed to enable a imx53 low power idle
state.  This includes adding the imx53 gpc_dvfs clock and making a
common imx5_late_init function and initializing all imx53
 MACHINE_STATE late_init calls to imx5_late_init.

Signed-off-by: Robert Lee <rob.lee@linaro.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>