m68k: define syscall_get_arch()

syscall_get_arch() is required to be implemented on all architectures
in addition to already implemented syscall_get_nr(),
syscall_get_arguments(), syscall_get_error(), and
syscall_get_return_value() functions in order to extend the generic
ptrace API with PTRACE_GET_SYSCALL_INFO request.

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Paul Moore <paul@paul-moore.com>
Cc: Elvira Khabirova <lineprinter@altlinux.org>
Cc: Eugene Syromyatnikov <esyr@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-audit@redhat.com
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>