drm/amdgpu: force pa_sc_tile_steering_override to 0 for gfx10.3

pa_sc_tile_steering_override is only programmable for
gfx10.0/10.1/10.2

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Likun Gao <Likun.Gao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>