Suspend-to-idle timer quiescing support for v3.20-rc1

Till now suspend-to-idle has not been able to save much more energy
than runtime PM because of timer interrupts that periodically bring
CPUs out of idle while they are waiting for a wakeup interrupt.  Of
course, the timer interrupts are not wakeup ones, so the handling of
them can be deferred until a real wakeup interrupt happens, but at
the same time we don't want to mass-expire timers at that point.

The solution is to suspend the entire timekeeping when the last CPU
is entering an idle state and resume it when the first CPU goes out
of idle.  That has to be done with care, though, so as to avoid
accessing suspended clocksources etc. end we need extra support
from idle drivers for that.

This series of commits adds support for quiescing timers during
suspend-to-idle and adds the requisite callbacks to intel_idle
and the ACPI cpuidle driver.

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