drm/amd/display: refactor ddc logic from dc_link_ddc to link_ddc

[why]
1. Move dd_link_ddc functions to link_ddc.
2. Move link ddc functions declaration exposed in dc to link.h
3. Move link ddc functions declaration exposed in dm to dc_link.h
4. Remove i2caux_interface.h file

Tested-by: Daniel Wheeler <Daniel.Wheeler@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>