drm/amdgpu: skip gpu_info firmware if discovery info is available

The GPU info firmware is only applicable at bring up when the
IP discovery table is not present.  If it's available, use that
first and then fallback to parsing the gpu info firmware.

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>