ARM: omap4.dtsi: add omapdss information

Add DT data for OMAP4 display subsystem, which contains the following
blocks:

dss - the wrapper/glue for the display modules
dispc - display controller
dsi - MIPI DSI encoder (two independent modules)
rfbi - MIPI DBI encoder
venc - analog TV encoder
hdmi - HDMI encoder

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>