Add bf16/fp16 support for amp with mps device #5400

Job	Run time
run-tests (latest, test_prod)	4m 3s
run-tests (latest, test_core)	4m 58s
run-tests (latest, test_cli)	2m 35s
run-tests (latest, test_big_modeling)	2m 19s
run-tests (latest, test_deepspeed)	2m 20s
run-tests (latest, test_fsdp)	2m 23s
run-tests (latest, test_example_differences)	4m 57s
run-tests (latest, test_checkpoint_step)	3m 51s
run-tests (latest, test_checkpoint_epoch)	3m 33s
run-tests (latest, test_rest)	11m 26s
run-tests (minimum, test_prod)	3m 24s
run-tests (minimum, test_core)	4m 14s
run-tests (minimum, test_cli)	3m 50s
run-tests (minimum, test_big_modeling)	3m 25s
run-tests (minimum, test_deepspeed)	3m 21s
run-tests (minimum, test_fsdp)	3m 38s
run-tests (minimum, test_example_differences)	3m 27s
run-tests (minimum, test_checkpoint_step)	4m 42s
run-tests (minimum, test_checkpoint_epoch)	6m 42s
run-tests (minimum, test_rest)	10m 35s
	1h 29m 43s

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