cmd/internal/obj/loong64: add {V,XV}DIV{B/H/W/V}[U] and {V,XV}MOD{B/H/W/V}[U] instruc...

cmd/internal/obj/loong64: add {V,XV}DIV{B/H/W/V}[U] and {V,XV}MOD{B/H/W/V}[U] instructions support

Go asm syntax:
	 VDIV{B/H/W/V}[U]	VK, VJ, VD
	XVDIV{B/H/W/V}[U]	XK, XJ, XD
	 VMOD{B/H/W/V}[U]	VK, VJ, VD
	XVMOD{B/H/W/V}[U]	XK, XJ, XD

Equivalent platform assembler syntax:
	 vdiv.{b/h/w/d}[u]	vd, vj, vk
	xvdiv.{b/h/w/d}[u]	xd, xj, xk
	 vmod.{b/h/w/d}[u]	vd, vj, vk
	xvmod.{b/h/w/d}[u]	xd, xj, xk

Change-Id: I3676721c3c415de0f2ebbd480ecd1b2400a28dba
Reviewed-on: https://go-review.googlesource.com/c/go/+/636376
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>