drm/amd/display: Use physical addressing for DMCUB on both dcn20/21

[Why]
CW0 and CW1 need to use physical addressing mode for dcn20 and dcn21.

The current code for dcn20 is using virtual.

[How]
We already program the DMCUB like this on dcn21 so we should just use
the same sequence for both.

Copy the dcn21 sequences into the dmjub_dcn20.c file and rename them.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>