drm/amdgpu/discovery: optionally use fw based ip discovery

On chips without native IP discovery support, use the fw binary
if available, otherwise we can continue without it.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Flora Cui <flora.cui@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>