timekeeping: utilize the suspend-nonstop clocksource to count suspended time

There are some new processors whose TSC clocksource won't stop
during
suspend. Currently, after system resumes, kernel will use
persistent
clock or RTC to compensate the sleep time, but with these
nonstop
clocksources, we could skip the special compensation from
external
sources, and just use current clocksource for time
recounting.

This can solve some time drift bugs caused by some
not-so-accurate or
error-prone RTC devices.

The current way to count
suspended time is first try to use the persistent
clock, and then try
the RTC if persistent clock can't be used. This
patch will change the
trying order to:
 suspend-nonstop clocksource -> persistent clock ->
RTC

When counting the sleep time with nonstop clocksource, use an
accurate way
suggested by Jason Gunthorpe to cover very large delta
cycles.

CRs-fixed: 536881
Change-Id:
I59c21b1ce5ae81cebc8cf3e817d9b3f951302a3d
Signed-off-by: Feng Tang
<feng.tang@intel.com>
[jstultz: Small optimization, avoiding re-reading
the clocksource]
Signed-off-by: John Stultz
<john.stultz@linaro.org>
Git-repo:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Git-commit:
e445cf1)
[sboyd: Took tk and clock local variables]
Signed-off-by:
Stephen Boyd <sboyd@codeaurora.org>

idea is taken here -
https://github.com/jrior001/android_kernel_samsung_d2/commit/02ea82befff0dc36547e3da345b3e81bf27a7c68