The DSS related clock muxes are set via assigned-clocks in a way which
provides us:

VP0 - DisplayPort SST
VP1 - DPI0
VP2 - DSI
VP3 - DPI1
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>