SF TimeStats: fix a display on time logic bug

When TimeStats is disabled, dumpsys should not flush extra display on
time into the stats. Also, update the present to present histogram to
only collect stats when display is on power mode normal.

Bug: b/79872109
Test: dumpsys SurfaceFlinger --timestats <options>
Change-Id: Id8d5ce83e5b303acaf9ba9fcf2fb6fb9518683f7