Move ch ring placement back from old FnLB. (#930)

* fn: bring back CH ring placer into FN repo based on original FnLB
* fn: move placement code into runnerpool directory

vendor/github.com/dchest/siphash/hash_asm.go

@@ -0,0 +1,33 @@
+// +build arm amd64,!appengine,!gccgo
+
+// Written in 2012 by Dmitry Chestnykh.
+//
+// To the extent possible under law, the author have dedicated all copyright
+// and related and neighboring rights to this software to the public domain
+// worldwide. This software is distributed without any warranty.
+// http://creativecommons.org/publicdomain/zero/1.0/
+
+// This file contains a function definition for use with assembly implementations of Hash()
+
+package siphash
+
+//go:noescape
+
+// Hash returns the 64-bit SipHash-2-4 of the given byte slice with two 64-bit
+// parts of 128-bit key: k0 and k1.
+func Hash(k0, k1 uint64, b []byte) uint64
+
+//go:noescape
+
+// Hash128 returns the 128-bit SipHash-2-4 of the given byte slice with two
+// 64-bit parts of 128-bit key: k0 and k1.
+func Hash128(k0, k1 uint64, b []byte) (uint64, uint64)
+
+//go:noescape
+func blocks(d *digest, p []uint8)
+
+//go:noescape
+func finalize(d *digest) uint64
+
+//go:noescape
+func once(d *digest)