userfaultfd: register uapi generic syscall (aarch64)

userfaultfd: register uapi generic syscall (aarch64)

Orabug: 21685254

Add the userfaultfd syscalls to uapi asm-generic, it was tested with
postcopy live migration on aarch64 with both 4k and 64k pagesize
kernels.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 09f7298100ea9767324298ab0c7979f6d7463183)
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Dhaval Giani <dhaval.giani@oracle.com>
Conflicts:
	include/uapi/asm-generic/unistd.h

Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>