drm/amdgpu: do not init mec2 jt for renoir

For ASICs like renoir/arct, driver doesn't need to load mec2 jt.
when mec1 jt is loaded, mec2 jt will be loaded automatically
since the write is actaully broadcasted to both.

We need to more time to test other gfx9 asic. but for now we should
be able to draw conclusion that mec2 jt is not needed for renoir and
arct.

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