cpufreq: pxa: use generic platdev driver for device-tree

For device-tree based pxa25x and pxa27x platforms, cpufreq-dt driver is
doing the job as well as pxa2xx-cpufreq, so add these platforms to the
compatibility list.

This won't work for legacy non device-tree platforms where
pxa2xx-cpufreq is still required.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>