drm/amdgpu: guard ras debugfs creation/removal based on CONFIG_DEBUG_FS

It can avoid potential build warn/error when
CONFIG_DEBUG_FS is not set.

Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Dennis Li <Dennis.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>