cmd/internal/obj/loong64: add {V,XV}ILV{L/H}.{B/H/W/D} instructions support

cmd/internal/obj/loong64: add {V,XV}ILV{L/H}.{B/H/W/D} instructions support

Go asm syntax:
	 VILV{L/H}{B/H/W/V}	VK, VJ, VD
	XVILV{L/H}{B/H/W/V}	XK, XJ, XD

Equivalent platform assembler syntax:
	 vilv{l/h}.{b/h/w/d}	vd, vj, vk
	xvilv{l/h}.{b/h/w/d}	xd, xj, xk

Change-Id: I40e21737649d9fdbbc9a423e859f4c0a56d069fb
Reviewed-on: https://go-review.googlesource.com/c/go/+/635936
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Junyang Shao <shaojunyang@google.com>