Thanks to some great debugging work by Olaf Hering and Marcus Meissner
it has been noticed that the current ppc64 syscall code is corrupting
4 bytes past errno. Why we even bothered to set errno beats me, its
unusable in the kernel.

Since we had to reinstate the inline syscall code we can go back to
using it for those few syscalls that we call. Especially now with
Randy's syscall prototype cleanup we should be calling them directly
but we can do that sometime later.