staging/lustre: fix build error on non-x86 platforms

dump_trace() is only available on X86. Without it, Lustre's own
watchdog is broken. We can only dump current task's stack.

The client-side this code is much less likely to hit deadlocks and
it's probably OK to drop this altogether, since we hardly have any
ptlrpc threads on clients, most notable ones are ldlm cb threads
that should not really be blocking on the client anyway.

Remove libcfs watchdog for now, until the upstream kernel watchdog
can detect distributed deadlocks and dump other kernel threads.

Cc: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>