OMAPDSS: use platform_driver_probe for dsi/hdmi/rfbi/venc/dpi/sdi

Now that the core.c doesn't fail if output driver's init fails, we can
change the uses of platform_driver_register to platform_driver_probe.
This will allow us to use __init in the following patches.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>