internal/abi, internal/buildcfg: always enable register ABI on PPC64
In last cycle we developed register ABI for ARM64, enabled by
default as a GOEXPERIMENT. This cycle we turn it on all the time.
Later CLs will clean up fallback code.
Change-Id: Idac4dcff634791cbc3d30988052ecd742b55ab8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/394214
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com>