SF: Use default minimal refresh rate between frames

When calculating duplicate frames make sure the minimal period
is at least Fps(120).toPeriodNsecs(). It's not okay to use
min period equal to the max refresh rate at layer creation,
because the supported refresh rates can change. E.g. initially
it can be 24hz and later (bacause another display is plugged)
it can be 60hz, which will cause a lot of frames to be considered
as duplicates.

Bug: 159590486
Test: presubmit
Change-Id: I4424c05012925273ed6ea8254fb975bf8fe7d058