cmd/internal/obj/loong64: add [X]VSHUF4I.{B/H/W/D} instructions support

cmd/internal/obj/loong64: add [X]VSHUF4I.{B/H/W/D} instructions support

Go asm syntax:
	 VSHUF4I{B/H/W/V}	$1, V1, V2
	XVSHUF4I{B/H/W/V}	$2, X1, X2

Equivalent platform assembler syntax:
	 vshuf4i.{b/h/w/d}	v2, v1, $1
	xvshuf4i.{b/h/w/d}	x2, x1, $2

Change-Id: I6a847ccbd2c93432d87bd1390b5cf1508da06496
Reviewed-on: https://go-review.googlesource.com/c/go/+/658376
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>