when setting security_ntp_sync_rtc to true, chrony will sync rtc every
11 minutes.
using rtcfile + rtcautotrim locks access to rtc clock for other tools,
like hwclock or timedatectl so it's hard to validate that the clock is
really synced.
Change-Id: I72fd18d36ab139d7140281374b5c2b89f7cb460a
ef1b417032