drm/amd/display: Use dce_audio_create for DCE 6

drm/amd/display: Use dce_audio_create for DCE 6

The only difference between DCE 6 and other DCE versions is
that DCE 6 doesn't support DCCG_AUDIO_DTO2_USE_512FBR_DTO.
Recently a check was added to dce_aud_wall_dto_setup() to
check that. So now DCE 6 can just use dce_aud_wall_dto_setup()
just like other DCE versions.

Clean up DCE 6 specific audio functions which were otherwise
identical to the rest.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rodrigo Siqueira <siqueira@igalia.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>