drm/amdgpu: query aldebaran gfx_config through atomfirmware i/f

For ASICs that don't support ip discovery feature, query
gfx configuration through atomfirmware interface, rather
than gpu_info firmware.

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>