sched: Calculate max_possible_freq based on current policy->max

Conflicts:
	kernel/sched/core.c
cpufreq: cpuboost: Always consider current policy max

We fixed calculations in the scheduler in 58cd101c69c508a448a03fc480ceb35f0da12386.
Now repeat this in the cpu-boost driver.

Conflicts:
	drivers/cpufreq/cpu-boost.c