We currently have omap_dss_device, which represents an external display
device, sometimes an external encoder, sometimes a panel. Then we have
omap_dss_output, which represents DSS's output encoder.

In the future with new display device model, we construct a video
pipeline from the display blocks. To accomplish this, all the blocks
need to be presented by the same entity.

Thus, this patch combines omap_dss_output into omap_dss_device. Some of
the fields in omap_dss_output are already found in omap_dss_device, but
some are not. This means we'll have DSS output specific fields in
omap_dss_device, which is not very nice. However, it is easier to just
keep those output specific fields there for now, and after transition to
new display device model is made, they can be cleaned up easier than
could be done now.

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