Utils part 1: create a separate buck target

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/551

The `utils` dir is broken down into two steps to deal with circular dependencies while keeping the diffs atomic. This diff creates TARGETS for the dirs. `utils`(except `demo_predictor.py`) and `utils/fb`. The TARGETS for `utils/testing` and `utils/demo_predictor.py` are introduced in down the stack in the diff D46096376.

Reviewed By: tglik

Differential Revision: D45912077

fbshipit-source-id: fb01969c5f5df97de8afaa24bee8492591059b4d

d2go/utils/flop_calculator.py

@@ -124,7 +124,9 @@ def add_flop_printing_hook(
 
 @PROFILER_REGISTRY.register()
 def default_flop_counter(model, cfg):
-    from d2go.trainer.fsdp import FSDP
+    from torch.distributed.fsdp.fully_sharded_data_parallel import (
+        FullyShardedDataParallel as FSDP,
+    )
 
     # TODO: deepcopy() not supported for FSDP yet (https://github.com/pytorch/pytorch/issues/82070), so we disable flop counter for now
     if isinstance(model, FSDP):