drm/omap: force runtime PM suspend on system suspend

Use SET_LATE_SYSTEM_SLEEP_PM_OPS in DSS submodules to force runtime PM
suspend and resume.

We use suspend late version so that omapdrm's system suspend callback is
called first, as that will disable all the display outputs after which
it's safe to force DSS into suspend.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200618095153.611071-1-tomi.valkeinen@ti.com
Acked-by: Tony Lindgren <tony@atomide.com>
Fixes: cef76630

 ("drm/omap: Prepare DSS for probing without legacy platform data")
Cc: stable@vger.kernel.org # v5.7+
Tested-by: Tony Lindgren <tony@atomide.com>