Faster GELU forward & backward using MUFU.TANH for SM7.5+ #1635

Job	Run time
build-cuda-fp16	1m 11s
build-cuda-bf16	1m 13s
build-cuda-fp32	1m 22s
build-and-test-cpu (ubuntu-latest)	4m 33s
build-cuda-kernels	1m 28s
build-and-test-cpu (macos-latest)	3m 13s
build-cuda-windows	2m 11s
build-ubuntu20-04	2m 36s
build-and-test-cpu (windows-latest)	7m 49s
	25m 36s

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