syscalls: make kcmp syscall available for all architectures

syscalls: make kcmp syscall available for all architectures

Remove the x86 dependency, since the system call is not architecture
dependent.

Also add a ptrace.h include, so it compiles at least also on s390.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>