runtime: implement cputicks with the stable counter on loong64

runtime: implement cputicks with the stable counter on loong64

The stable counter is described in Section 2.2.10.4, LoongArch Reference Manual Volume 1.

Ref: https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html

Change-Id: I160b695a8c0e38ef49b21fb8b41460fd23d9538c
Reviewed-on: https://go-review.googlesource.com/c/go/+/421656
Reviewed-by: Meidan Li <limeidan@loongson.cn>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Wayne Zuo <wdvxdr@golangcn.org>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Michael Pratt <mpratt@google.com>