Make the persistent clock check a kernel config option, so that some
platform can explicitely select it, also make CONFIG_RTC_HCTOSYS depends
on its non-existence, which could prevent the persistent clock and RTC
code from doing similar thing twice during system's init/suspend/resume
phases.
If the CONFIG_HAS_PERSISTENT_CLOCK=n, then no change happens for kernel
which still does the persistent clock check in timekeeping_init().
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Suggested-by: John Stultz <john.stultz@xxxxxxxxxx>
Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>