drm/amd/display: change dcn_ip and dcn_soc into pointers

-Change dcn_ip into pointer
-Change dcn_soc into pointer

This is needed for flattening of core_dc into dc, as without
this the diags build fails

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