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

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

Go asm syntax:
	 VMOVQ	offset(Rj), Vd.<T>
	XVMOVQ	offset(Rj), Xd.<T>

<T> can have the following values:
B16, H8, W4, V2, B32, H16, W8, V4

Change-Id: I44af51d58bb62649d3fe360b3abb771565e78a8a
Reviewed-on: https://go-review.googlesource.com/c/go/+/682895
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Meidan Li <limeidan@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mark Freeman <mark@golang.org>