drm/amdgpu: Add PCIe replay count sysfs file

Add a sysfs file for reporting the number of PCIe replays (NAKs). This
returns the sum of NAKs received and NAKs generated

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>