drm/omap: tiler: add hibernation callback

Setting a dev_pm_ops resume callback but not a set of hibernation
handler means that pm function will not be called upon hibernation.

Fix this by using SIMPLE_DEV_PM_OPS, which appropriately assigns the
suspend and hibernation handlers and move omap_dmm_resume under
CONFIG_PM_SLEEP to avoid build warnings.

Signed-off-by: Grygorii Strashko <grygorii.strashko@linaro.org>
Reviewed-by: Rob Clark <robdclark@gmail.com>
[tomi valkeinen: add missing 'static']
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>