cpufreq: dt: Allow platform specific suspend/resume callbacks

Platforms may need to implement platform specific suspend/resume hooks.
Update cpufreq-dt driver's platform data to contain those for such
platforms.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>