cpufreq: conservative: Add a switch to enable fast mode

driver inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I78PCH


CVE: NA

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Add a switch in conservative governor. If set 0(default), adopt slow
mode to pursue greater power consumption benefits; Otherwise set 1,
adopt fast mode to reduce performance loss.

Signed-off-by: Jiang Yi <jiangyi38@hisilicon.com>
Signed-off-by: xuesinian <xuesinian@huawei.com>