As the merge window is still open, and this code was not as complex

as I thought it might be. I'm pushing this in now.

This will allow Thomas to debug his irq work for 3.20.

This adds two new features:

1) Allow traceopoints to be enabled right after mm_init(). By passing
in the trace_event= kernel command line parameter, tracepoints can be
enabled at boot up. For debugging things like the initialization of
interrupts, it is needed to have tracepoints enabled very early. People
have asked about this before and this has been on my todo list. As it
can be helpful for Thomas to debug his upcoming 3.20 IRQ work, I'm
pushing this now. This way he can add tracepoints into the IRQ set up
and have users enable them when things go wrong.

2) Have the tracepoints printed via printk() (the console) when they
are triggered. If the irq code locks up or reboots the box, having the
tracepoint output go into the kernel ring buffer is useless for
debugging. But being able to add the tp_printk kernel command line
option along with the trace_event= option will have these tracepoints
printed as they occur, and that can be really useful for debugging
early lock up or reboot problems.

This code is not that intrusive and it passed all my tests. Thomas tried
them out too and it works for his needs.

 Link: http://lkml.kernel.org/r/20141214201609.126831471@goodmis.org
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