cmd/internal/obj/loong64: add VPERMI.W, XVPERMI.{W,V,Q} instruction support

cmd/internal/obj/loong64: add VPERMI.W, XVPERMI.{W,V,Q} instruction support

Go asm syntax:
	 VPERMIW        $0x1b, vj, vd
	XVPERMI{W,V,Q}  $0x1b, xj, xd

Equivalent platform assembler syntax:
	 vpermi.w       vd, vj, $0x1b
	xvpermi.{w,d,q} xd, xj, $0x1b

Change-Id: Ie23b2fdd09b4c93801dc804913206f1c5a496268
Reviewed-on: https://go-review.googlesource.com/c/go/+/716800
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Meidan Li <limeidan@loongson.cn>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
Reviewed-by: Michael Knyszek <mknyszek@google.com>