cpufreq: Add new helper function returning cpufreq policy

cpufreq: Add new helper function returning cpufreq policy

cpufreq_cpu_get_raw() gets cpufreq policy only if the CPU is in
policy->cpus mask, which means the CPU is already online. But in some
cases, the policy is needed before the CPU is added to cpus mask. Add a
function to get the policy in these cases.

Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Reviewed-by: Jie Zhan <zhanjie9@hisilicon.com>
Acked-by: Beata Michalska <beata.michalska@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>