ARM: bcm2835: perf_event support for Raspberry-Pi

ARM: bcm2835: perf_event support for Raspberry-Pi

The following patch enables performance counter support on Raspberry-Pi.

We have this working on the 2708 based rasp-pi kernels by manually putting
the device registration in the platform files.

This change does things properly in a device tree.  The boot messages look
proper, but my rasp-pi hangs somewhere in USB enabling when running a
stock 3.13-rc6 kernel so I have been unable to fully test this change.

I also understand that the rasp-pi 1176 pmu support is missing the
overflow interrupt.  I'm not sure if that's true of all 2835
implementations.  If not, then this patch will need to be changed a bit.

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
[swarren, fixed DT node sort order]
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>