MAINTAINERS: Add entries for Apple SoC cpufreq driver

This MAINTAINERS update is split, as usual, to facilitate merges via the
SoC tree and avoid conflicts.

Acked-by: Marc Zyngier <maz@kernel.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Hector Martin <marcan@marcan.st>