drm/amdgpu/display: fix build when CONFIG_DEBUG_FS is not set

amdgpu_dm_crtc_late_register() is only used when CONFIG_DEBUG_FS
is enabled so make it dependent on that.

Fixes: 4cd79f61

 ("drm/amd/display: Move connector debugfs to drm")
Cc: Bhanuprakash Modem <bhanuprakash.modem@intel.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Arun R Murthy <arun.r.murthy@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Tested-by: Nathan Chancellor <nathan@kernel.org> # build
Link: https://lists.freedesktop.org/archives/dri-devel/2022-June/359496.html
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220615210019.28943-1-alexander.deucher@amd.com