timekeeping: Ignore the bogus sleep time if pm_trace is enabled

Power management suspend/resume tracing (ab)uses the RTC to store
suspend/resume information persistently. As a consequence the RTC value is
clobbered when timekeeping is resumed and tries to inject the sleep time.

Commit a4f8f6667f09 ("timekeeping: Cap array access in timekeeping_debug")
plugged a out of bounds array access in the timekeeping debug code which
was caused by the clobbered RTC value, but we still use the clobbered RTC
value for sleep time injection into kernel timekeeping, which will result
in random adjustments depending on the stored "hash" value.

To prevent this keep track of the RTC clobbering and ignore the invalid RTC
timestamp at resume. If the system resumed successfully clear the flag,
which marks the RTC as unusable, warn the user about the RTC clobber and
recommend to adjust the RTC with 'ntpdate' or 'rdate'.

[jstultz: Fixed up pr_warn formating, and implemented suggestions from Ingo]
[ tglx: Rewrote changelog ]

Originally-from: Thomas Gleixner <[email protected]>
Signed-off-by: Chen Yu <[email protected]>
Signed-off-by: John Stultz <[email protected]>
Acked-by: Pavel Machek <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Cc: Prarit Bhargava <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Richard Cochran <[email protected]>
Cc: Xunlei Pang <[email protected]>
Cc: Len Brown <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

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