drm/amdgpu: Add NBIO SMN headers v2

We need these offsets for PCIE perf counters, so include them as well as
the the previously-used defines from the nbio_*.c files

v2: Return NBIF definitions back to previous files

Signed-off-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>