tracing: Have ftrace_dump_on_oops kernel parameter take numbers

The kernel parameter for ftrace_dump_on_oops can take a single assignment.
That is, it can be:

  ftrace_dump_on_oops or ftrace_dump_on_oops=orig_cpu

But the content in the sysctl file is a number.

 0 for disabled
 1 for ftrace_dump_on_oops (all CPUs)
 2 for ftrace_dump_on_oops (orig CPU)

Allow the kernel command line to take a number as well to match the sysctl
numbers.

That is:

  ftrace_dump_on_oops=1 is the same as ftrace_dump_on_oops

and

  ftrace_dump_on_oops=2 is the same as ftrace_dump_on_oops=orig_cpu

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>