[PATCH] 3/5 powerpc: Add platform functions interpreter

This is the platform function interpreter itself along with the backends
for UniN/U3/U4, mac-io, GPIOs and i2c. It adds the ability to execute
those do-platform-* scripts in the device-tree (at least for most
devices for which a backend is provided). This should replace the clock
spreading hacks properly. It might also have an impact on all sort of
machines since some of the scripts marked "at init" will now be executed
on boot (or some other on sleep/wakeup), those will possibly do things
that the kernel didn't do at all, like setting some values into some i2c
devices (changing thermal sensor calibration or conversion rate) etc...
Thus regression testing is MUCH welcome. Also loook for errors in dmesg.
That's also why I've left rather verbose debugging enabled in this
version of the patch.

(I do expect some Windtunnel G4s to show some errors as they have an i2c
clock chip on the PMU bus that uses some primitives that the i2c backend
doesn't implement yet. I really need users that have one of those
machine to come back to me so we can get that done right, though the
errors themselves should be harmless, I suspect the machine might not
run at full speed).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>