drm/amd/display: Allow cursor position when plane_res.ipp is NULL

[Why]
Starting with DCN1, the input_pixel_processor (ipp) struct has been
replaced by dpp struct (part of DAL3.1 SW architecture change).
Need to update logic to handle cases where ipp is never allocated.

[How]
Only skip cursor position programming if both ipp and dpp resources
are NULL.

Signed-off-by: Eric Bernstein <eric.bernstein@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>