thermal: imx: correct suspend/resume flow

Fixes regression introduced by:

commit 37713a1e
Author: Philipp Zabel <p.zabel@pengutronix.de>
Date:   Thu Aug 1 18:33:12 2013 +0200

    thermal: imx: implement thermal alarm interrupt handling

The commit 37713a1e makes imx thermal sensor always powered up as alarm
function is enabled, but the suspend callback of imx thermal returns
success only if thermal sensor is powered down, so it will always returns
fail hence break system's suspend, this patch disables imx thermal sensor
before suspend and re-enable it after resume.

Signed-off-by: Anson Huang <b20788@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>