Switch to NO_HZ_IDLE for energy saving. Also enable Menu cpuidle
governor for tickless systems.
Run-tested: Linksys WRT1900AC v2
Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21136
Signed-off-by: Robert Marko <robimarko@gmail.com>