dc_target does not fit well into DRM framework so removed it.
This will prevent the driver from leveraging the pipe-split
code for tiled displays, so will have to be handled at a higher
level.  Most places that used dc_target now directly use dc_stream
instead.
Signed-off-by: NAric Cyr <aric.cyr@amd.com>
Acked-by: NHarry Wentland <Harry.Wentland@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>