cmd/asm: add amd64 PAB{SB,SD,SW}, PMADDUBSW, PMULHRSW, PSIG{NB,ND,NW}

cmd/asm: add amd64 PAB{SB,SD,SW}, PMADDUBSW, PMULHRSW, PSIG{NB,ND,NW}

instructions

1st change out of 3 to cover AMD64 SSSE3 instruction set in Go asm.
This commit adds instructions that do not require new named ytab sets.

Change-Id: I0c3dfd8d39c3daa8b7683ab163c63145626d042e
Reviewed-on: https://go-review.googlesource.com/56834
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>
Reviewed-by: Russ Cox <rsc@golang.org>