drm/omap: add new connector types

We have been using DRM_MODE_CONNECTOR_Unknown for many of our outputs
because there has not been a proper connector type for them.

We now have connector type for DPI so let's take it into use. At the
same time, add better connector types for the remaining outputs too.

This patch sets the following outputs to use the following connector
types:

DPI -> DPI
DBI -> DPI (MIPI DBI is very similar to DPI at the bus level)
SDI -> LVDS (SDI, TI Flatlink 3G, is a type of LVDS)
VENC -> SVIDEO or Composite

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