drm/amdgpu: set gfx9 onwards APU atomics support to be true

APUs w/ gfx9 onwards doesn't reply on PCIe atomics, rather
it is internal path w/ native atomic support. Set have_atomics_support
to true.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Reviewed-by: Lang Yu <lang.yu@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>