drm/amdgpu: Add replay counter defines to NBIO headers

Add the PCIE_RX_NUM_NACK and PCIE_RX_NUM_NACK_GENERATED values to the
NBIO SMN headers in preparation for exposing the number of PCIe replays
via sysfs

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