ARM: add IPI tracepoints

The strings used to list IPIs in /proc/interrupts are reused for tracing
purposes.

While at it, prevent a negative ipinr from escaping the range check
in handle_IPI().

Link: http://lkml.kernel.org/p/1406318733-26754-4-git-send-email-nicolas.pitre@linaro.org



Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>