cpufreq: armada-8k: make both cpu masks static

An earlier patch marked one of the two CPU masks as 'static' to reduce stack
usage, but if CONFIG_NR_CPUS is large enough, the function still produces
a warning for compile testing:

drivers/cpufreq/armada-8k-cpufreq.c: In function 'armada_8k_cpufreq_init':
drivers/cpufreq/armada-8k-cpufreq.c:203:1: error: the frame size of 1416 bytes is larger than 1408 bytes [-Werror=frame-larger-than=]

Normally this should be done using alloc_cpumask_var(), but since the
driver already has a static mask and the probe function is not called
concurrently, use the same trick for both.

Fixes: 1ffec650 ("cpufreq: armada-8k: Avoid excessive stack usage")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>