x86, ftrace: Use safe noops, drop trap test

Always use a safe 5-byte noop sequence.  Drop the trap test, since it
is known to return false negatives on some virtualization platforms on
32 bits.  The resulting code is both simpler and safer.

Cc: Daniel Drake <dsd@laptop.org>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>