cmd/compile: move loong64 over to new bounds check strategy

cmd/compile: move loong64 over to new bounds check strategy

Change-Id: I5dec33d10d16a5d5c0dc7231cd1f764a6d1d7598
Reviewed-on: https://go-review.googlesource.com/c/go/+/682399
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>