add grad_scaler and bf16 support. #1625

Job	Run time
atorch-python-test	7m 0s
atorch-pre-commit	4m 51s
brain-test	2m 52s
dlrover-client-test	2m 53s
dlrover-python-test	3m 29s
dlrover-system-test-criteo-deeprec	3m 24s
dlrover-system-test-deepfm	3m 27s
dlrover-system-test-tf2	1m 58s
dlrover-trainer-test	2m 33s
operator-test	2m 15s
pre-commit	15m 8s
tfplus-pre-commit	57s
tfplus-python-test	1m 5s
	51m 52s

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