ARM: dts: Add Integrator/CP cpus node and operating points

This adds the cpus node to the Integrator/CP device tree so
that we have a proper placeholder to put in the DT-defined
operating points for the generic DT/OPP cpufreq driver,
along with two working operating points.

I have only put in 48 and 50 MHz because going to e.g. 36
MHz hangs the system when CLCD graphics are active.
Presumably the memory bus gets to slow to feed the display
and the systems hangs for this reason. The ideal solution
would be for the display controller to put constraints on
the memory bus frequency, but that need to be a separate
longer-term project.

We define a CPU node since this is required for cpufreq-dt,
however we do not define any compatible string for the CPU
since this architecture has pluggable CPU modules and we
do not know which one will be used. If necessary, the CPU
compatible can be filled in by the boot loader, but for
just cpufreq-dt it is not required.

Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>