cpufreq: ap806: fix cpufreq driver needs ap cpu clk

The Armada 8K cpufreq driver needs the Armada AP CPU CLK
to work. This dependency is currently not satisfied and
the ARMADA_AP_CPU_CLK can not be selected independently.

Add it to the cpufreq Armada8k driver.

Fixes: f525a670 ("cpufreq: ap806: add cpufreq driver for Armada 8K")
Signed-off-by: Sven Auhagen <sven.auhagen@voleatech.de>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>