drm/amd/display: Allow multiple instance of DTO regs

Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Reviewed-by: Jordan Lazare <Jordan.Lazare@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>