Update syscall lists for Linux 5.6

[Dmitry V. Levin]

On Wed, Apr 01, 2020 at 05:08:11PM +0000, Joseph Myers wrote:
> Linux 5.6 has new openat2 and pidfd_getfd syscalls.  This patch adds
> them to syscall-names.list and regenerates the arch-syscall.h files.

LGTM, thanks,


-- 
ldv