These FP registers on PPC64 have no restrictions, they can
be used like the others. F27-F31 were sequested long ago for
scratch storage which has long since been reverted, but they
weren't added back to the allocator pool.
Change-Id: I9074660e2fc91a2044c9768f700a8215802cba51
Reviewed-on: https://go-review.googlesource.com/c/go/+/395834
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>
Trust: Lynn Boger <laboger@linux.vnet.ibm.com>