drm/amd/display: Create dm_plane_state.

Hook up dc_surface creation/destruction to dm_plane_state.
Rename amdgpu_drm_plane_state to dm_plane_state and do
minor cleanups.

Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>