x86, sched: Move check for CPU type to caller function

Improve readability of the function intel_set_max_freq_ratio() by moving
the check for KNL CPUs there, together with checks for GLM and SKX.

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lkml.kernel.org/r/20200416054745.740-5-ggherdovich@suse.cz