centralize all debugfs creation in one place for ras

this is required to fix ras when the driver does not use the drm load
and unload callbacks due to ordering issues with the drm device node.
Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Stanley.Yang <Stanley.Yang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>