OMAPDSS: fix use of dssdev->caps

Recent commit dca2b152 (OMAPDSS: DSI:
Maintain copy of operation mode in driver data) broke DSI for video mode
displays. The commit changed the way dssdev->caps are initialized, and
the result was that every DSI display is initialized with manual-update
and tear-elim caps.

The code that sets dssdev->caps is not very good, even when fixed.
omapdss driver shouldn't be writing dssdev->caps at all.

This patch fixes the problem with video mode displays by moving the
initialization of dssdev->caps to the panel driver. The same change is
done for RFBI.

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