drm/amdgpu: Calculate IP specific xgmi bandwidth

Use IP version specific xgmi speed/width for bandwidth calculation.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Jonathan Kim <jonathan.kim@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>