runtime: cleanup ppc64le/linux library startup code

runtime: cleanup ppc64le/linux library startup code

Fix the argument passing to runtime.newosproc0, the ABI0 argument
storing must account for the fixed frame size.

Cleanup the _rt0_ppc64le_linux_lib definition, the assembler
should not generate a stack frame.  And convert it to use the
new ABI wrappers.

Change-Id: Ibc0be8b37f6522900781a19980fa018dd89ba7b3
Reviewed-on: https://go-review.googlesource.com/c/go/+/479796
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Paul Murphy <murp@ibm.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>