var crypto/sha256.useAVX2

one use

	crypto/sha256 (current package)
		sha256block_amd64.go#L9: var useAVX2 = cpu.X86.HasAVX2 && cpu.X86.HasBMI2

The pages are generated with Golds v0.4.9. (GOOS=linux GOARCH=amd64)