drm/amdgpu: Add compile flag for securedisplay

Add compile flag CONFIG_DEBUG_FS to clear the warning:
unused variable 'amdgpu_securedisplay_debugfs_ops'

Signed-off-by: Jinzhou Su <Jinzhou.Su@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>