var crypto/sha512.useAVX2

2 uses

	crypto/sha512 (current package)
		sha512block_amd64.go#L17: var useAVX2 = cpu.X86.HasAVX2 && cpu.X86.HasBMI1 && cpu.X86.HasBMI2
		sha512block_amd64.go#L20: 	if useAVX2 {