cmd/internal/obj/arm: support more ARM VFP instructions

cmd/internal/obj/arm: support more ARM VFP instructions

Add support of more ARM VFP instructions in the assembler.
They were introduced in ARM VFPv2.

"NMULF/NMULD   Fm, Fn, Fd": Fd = -Fn*Fm
"MULAF/MULAD   Fm, Fn, Fd": Fd = Fd + Fn*Fm
"NMULAF/NMULAD Fm, Fn, Fd": Fd = -(Fd + Fn*Fm)
"MULSF/MULSD   Fm, Fn, Fd": Fd = Fd - Fn*Fm
"NMULSF/NMULSD Fm, Fn, Fd": Fd = -(Fd - Fn*Fm)

Change-Id: Icd302676ca44a9f5f153fce734225299403c4163
Reviewed-on: https://go-review.googlesource.com/60170
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>