drm/amdgpu/uvd3.x: fix register definition warnings

drop the duplicate register macros from sid.h and use the
standard ones in the oss register headers.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>