drm/amd/display: allow query ddc data over aux to be read only operation

[why]
Two issues:
1. Add read only operation support for query ddc data over aux.
2. Fix a bug where if read size is multiple of 16,
mot of the last read transaction will not be set to 0.

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