OMAPDSS: remove initial display code from omapdss

OMAPDSS: remove initial display code from omapdss

Currently omapdss driver sets up the initial connections between
overlays, overlay manager and a panel, based on default display
parameter coming from the board file or via module parameters.

This is unnecessary, as it's the higher level component that should
decide what display to use and how. This patch removes the code from
omapdss, and implements similar code to omapfb.

The def_disp module parameter and the default display platform_data
parameter are kept in omapdss, but omapdss doesn't do anything with
them. It will just return the default display name with
dss_get_default_display_name() call, which omapfb uses. This is done to
keep the backward compatibility.

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