runtime: save and restore all fcc registers in async preempt on loong64
Currently, all Op implementations on loong64 use fcc0 by default, so only
fcc0 is saved in CL 475577. However, fcc1-fcc7 may also be used by users
when writing assembly code, such as in CL 693878.
Change-Id: Idb60d8101a0f7d602dfcbbb39bd5da9f2c475bfd
Reviewed-on: https://go-review.googlesource.com/c/go/+/696875
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn> Reviewed-by: Meidan Li <limeidan@loongson.cn> Reviewed-by: Carlos Amedee <carlos@golang.org>