drm: ti-lcdc: add missing pm_runtime_put_sync()

we need to make sure device is runtime suspended
before disabling pm_runtime.

Signed-off-by: Felipe Balbi <balbi@ti.com>
drm: ti-lcdc: add a workqueue for drm_flip_work_commit()

Signed-off-by: Felipe Balbi <balbi@ti.com>