Port mksyscall_aix_ppc64.pl Perl script to mksyscall_aix_ppc64.go.
mkall.sh script is modified to run mksyscall.go. Running
mkall.sh does not generate any git diff besides the command
name in comments of generated files.

Updates golang/go#27779

Change-Id: Ie888c0df470dcfc75034faa12cf3422b2d426629
Reviewed-on: https://go-review.googlesource.com/c/158699
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>