cpufreq: replace cpumask_weight with cpumask_empty where appropriate

drivers/cpufreq calls cpumask_weight() to check if any bit of a given
cpumask is set. We can do it more efficiently with cpumask_empty() because
cpumask_empty() stops traversing the cpumask as soon as it finds first set
bit, while cpumask_weight() counts all bits unconditionally.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com> (for SCMI cpufreq driver)
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>